Why people cheat, and why infidelity no longer matters in a Swiss divorce

A significant share of the requests a private investigator receives concern the same suspicion: is my partner cheating on me?

Before talking about investigations, I think it is right to answer two questions that come first. The first is why people cheat, and here it pays to listen to research more than to clichés. The second is what use, in practice, proof of infidelity has in Switzerland. The answer surprises many: in most cases, before a divorce judge, it is of no use at all.

I write this out of honesty, the same honesty I bring to the first consultation: in many cases an infidelity investigation has emotional value, not legal value. Sometimes it is legitimate to want one anyway. But it is right to know beforehand.

Why people cheat: what research says

Eight recurring motivations

One of the most cited studies on the subject was carried out by Dylan Selterman (University of Maryland), Justin Garcia (Indiana University) and Irene Tsapelas, and published in the Journal of Sex Research. The researchers asked 562 adults who had been unfaithful in a committed relationship to describe their reasons (University of Maryland).

Eight motivations emerged:

The first five concern the couple; the last three mainly concern the person and the context. That is an important point: not every affair comes from a relationship in crisis. As Selterman himself observed, we often hear that infidelity is a symptom of a damaged relationship, but people cheat for many reasons, and not all of them reflect the health of the couple.

Men and women: where the differences are

The study found some differences, which are worth reporting precisely:

• men more often cited sexual desire, variety and circumstances;
• women more often cited feeling neglected.

These are tendencies, not rules. All eight motivations appear in both sexes, and they often combine in the same person. Anyone searching for "why women cheat" or "why men cheat" will find a less clear-cut answer in the research than they expect.

The motive says a lot about the kind of affair

A second study by the same authors, published in 2021 with a sample of 495 people, showed that motivations help predict what kind of affair develops (PsyPost):

• those who cheat out of lack of love or because they feel neglected tend to have longer, more intimate and more emotionally involving affairs;
• those who cheat because of occasional circumstances have shorter, less intimate and less satisfying affairs;
• those who cheat out of anger or low commitment are more likely to leave their partner;
• those who cheat out of anger are also more likely to confess.

In other words, "infidelity" is a single word for very different realities: a night after a party and a parallel relationship lasting years have almost nothing in common, either for those who live them or for those who suffer them.

How common it is, and who cheats more

The most solid data come from the United States. According to an analysis of the General Social Survey published by the Institute for Family Studies in 2018, 20% of married men and 13% of married women said they had had sex with someone other than their spouse while married (Institute for Family Studies).

The most interesting figure is another: among 18- to 29-year-olds the gap disappears, and women slightly exceed men, 11% to 10%. The gender difference opens up with age and is widest in the oldest groups.

Two cautions. These are American data, and I found no comparable, reliable Swiss statistics. And they rely on what people are willing to declare: on a subject like this, honest answers cannot be taken for granted.

In Switzerland, fault no longer counts in divorce

Now to the legal side, which most often surprises people who come to me.

Since 2000, no-fault divorce

On 1 January 2000 the new divorce law came into force. The principle is clear: the conditions and consequences of divorce are settled without considering either spouse's fault (Federal Office of Justice, in Italian).

This means divorce is possible:

• on joint request of the spouses;
• on the request of one spouse, after two years of separation;
• before two years only if, for serious reasons not attributable to the applicant, continuing the marriage cannot reasonably be expected (art. 115 Civil Code). This is an exception, assessed case by case by the court.

The duty of fidelity still exists: the Civil Code states that spouses owe each other fidelity and assistance (art. 159 Civil Code). But breaching it does not, in itself, have consequences in divorce.

Maintenance is not a punishment

Post-divorce maintenance does not depend on who is "at fault". The court looks at objective criteria (art. 125 Civil Code): how tasks were divided during the marriage, its length, the standard of living, age and health, income and assets, childcare, training and career prospects, pensions.

Maintenance can exceptionally be refused or reduced only where it would be manifestly unfair, in particular if the person claiming it:

1. seriously breached their duty to contribute to the family's maintenance;
2. deliberately caused their own state of need;
3. committed a serious offence against the other spouse or someone close to them.

Infidelity, in itself, is not on this list.

Pensions and children

The splitting of occupational pension assets also takes place regardless of the reasons for the divorce. And for children there is a single criterion: the child's welfare (art. 133 Civil Code). An unfaithful parent is not, for that reason, a bad parent in the eyes of the court.

When an investigation still makes legal sense

There are, however, situations in which a professional inquiry can carry real weight.

1. The former spouse's stable cohabitation

This is the most frequent case. If the former spouse receiving maintenance lives with a new partner in a stable relationship, maintenance can be reduced or even cancelled.

The Federal Supreme Court defines qualified cohabitation as a lasting, exclusive life partnership with emotional, physical and economic components: in essence, a relationship offering the same fidelity and assistance as a marriage. If the cohabitation has already lasted five years when proceedings begin, it is presumed to be qualified; the presumption can be rebutted, though, and maintenance can be cancelled even before five years if other factors show the relationship is stable. It is up to the paying spouse to make the situation credible (judgment 5A_852/2019, in Italian, citing BGE 138 III 97).

Recent case law has become stricter in recognising cohabitation as qualified, for instance when the two partners remain financially independent (commentary on judgment 5A_127/2023). That is exactly why documented facts are needed: for how long, how stable, how much of home and expenses are shared. An impression is not enough.

2. The children's welfare

Not infidelity in itself, but behaviour that puts the children at risk: neglect, dangerous environments, company that exposes the child to real risks. Here documentation can carry weight in decisions on custody and contact.

3. Hidden income and assets

Maintenance is calculated on income and assets. If the other spouse is suspected of hiding an activity, income or property, the inquiry is no longer about infidelity but about the financial situation. It is work close to the asset searches I carry out for creditors and law firms.

4. Serious situations

Threats, violence, offences against the spouse or family members. Here the priority is safety, and the first point of contact is the police or a lawyer, not an investigator.

The limits not to cross

Even when an inquiry makes sense, it must respect the law. I have written about this in more detail in the article on surveillance and what the law says, but some points bear repeating:

• secretly reading your partner's messages, installing spyware or recording private conversations is not a way to obtain evidence: it exposes you to criminal and civil liability;
• observation in public places is allowed only within limits of proportionality, respecting personality rights (art. 28 Civil Code) and data protection law;
• in civil proceedings, unlawfully obtained evidence is considered only if the interest in establishing the truth prevails (art. 152 para. 2 Civil Procedure Code). Building a case on badly gathered material is a bet that usually fails.

And when the reason is purely emotional?

This is the most delicate point. Many people do not want evidence for a judge: they want to know. To end a doubt that wears them down, to decide whether to stay or leave, to stop being told it is all in their head.

It is a legitimate need, and I do not judge it. But before commissioning an investigation it is worth asking three questions:

1. What will I do with the answer? If the decision is already made, the investigation may not be needed. If it is not, it is worth asking whether the answer will really make it easier.
2. What answer would reassure me? Someone who has already decided their partner is cheating is often not convinced even by a report saying "nothing emerged". In that case the investigation costs money and resolves nothing.
3. Have I tried talking about it? Sometimes the problem is not another person but distance in the couple. Research confirms it: feeling neglected and lack of love are among the recurring motivations. A couples counsellor may be more useful than an investigator.

If after these questions the answer is still yes, a lawful, targeted and documented inquiry can give the clarity you are looking for. But whoever commissions it should know they are buying an answer for themselves, not a weapon for court.

How I work on these cases

The first consultation is free and confidential, and it serves precisely to understand whether an investigation makes sense. Sometimes the answer is no, and I say so before taking the case. When it does make sense, especially in cases of cohabitation or hidden income, you receive a written plan and a report that separates established facts from hypotheses, designed to be used by your lawyer.

You will find how an assignment works, the costs and the value of evidence in the guide on when you need a private investigator in Ticino, and the full conditions on the Fees and terms page.

This article provides general information and is no substitute for legal advice. Decisions on divorce, maintenance and children should be assessed with a lawyer, case by case.