Many family law clients ask if they should hire a private investigator to prove their spouses are cheating--probably because Canadians watch too many American legal TV shows. If you talk to any Toronto divorce lawyer (or any family law lawyer in Ontario, or anywhere else in Canada), he or she will tell you there are three possible reasons for which you can ask for a divorce: you have been separated for one year, one spouse was mentally or physically cruel to the other, or one spouse was unfaithful. In reality, though, the vast majority of people just use the first ground for divorce (being separated); whether someone has been unfaithful is rarely the reason they state in court to get divorced.
If you're not married, but just "spouses" because you lived together continuously for three or more years (that's the cut off for "common law" status in Ontario--it's only two years in BC) then there is only one reason why a relationship ends: because the people separate. Infidelity is not legally relevant. If you want to leave, you leave, regardless of the reason. Once we scratch off infidelity as a reason to spy on your spouse, there is usually no need to hire an investigator to find out what he or she is doing. It is usually not legally relevant. I don't mean to suggest that a person's infidelity is not important to his or her spouse. It is, and it's often the thing that leads to people "living separate and apart." But beyond that, your spouse's unfaithfulness will almost never matter in court. The Divorce Act explicitly prevents judges from considering "past conduct" of the spouses when making (or changing) custody orders unless the conduct is relevant to the person's ability to care for his or her child. That generally means it doesn't matter to a judge whether your spouse is having an affair. In Ontario, the Children's Law Reform Act, has the same general rule against considering "past conduct". If the past conduct involved domestic violence, then it might be relevant. But again, being unfaithful is usually not a good enough reason for a judge in Ontario (or BC) to conclude that a person cannot be a good parent. The Ontario Family Law Act does say that a judge can consider "past conduct" when deciding how much spousal support to award, but only if the conduct is "so unconscionable as to constitute an obvious and gross repudiation of the relationship."
Now, you might think that cheating on your spouse is a "gross repudiation of the relationship," but it is not. At least not legally speaking. To be a "gross repudiation of the relationship," the conduct must be much worse than a simple "matrimonial offence." So again, being unfaithful is not going to change things. (To make things worse, if you go down this road and cannot prove your spouse's conduct was "unconscionable" to the level the Family Law Act requires, you may be ordered to pay punitive costs at trial--judges do not want to hear about your spouse's affair.) There are some rare times when a person's conduct may be relevant to something in a family law case. If someone suffers from a serious drug addiction, for example, that might be something that prevents him or her from properly caring for a child. If that person is intent on hiding the addiction, in very rare cases, it might be worth hiring an investigator to get the evidence you need to prove that your child is unsafe with the other parent. More common, but still rare, is hiring a private investigator to prove financial facts: If your ex-spouse is living with his partner instead of on his own, it could affect his expenses. If your ex-spouse is getting paid under the table, an investigator may be able to prove it even if her bank account information doesn't show any income from the job. But take our word for it--hiring a private detective in a Toronto separation or divorce case is a very rare thing. So generally speaking, when clients start talking about wanting to hire private investigators to prove that their spouses are cheating on them, we have to tell them that it won't help them in court. Given the expense involved and the fact that spying on your spouse generally inflames emotions at an already difficult time, hiring a private detective is usually a bad idea. By the way: just because you shouldn't spy on your spouse doesn't mean you shouldn't worry about him or her spying on you--it is always a good idea when you separate to change your passwords on your phone, e-mail, and other online accounts. Again, your spouse probably won't benefit by spying on you, but no one likes to have his or her privacy violated. Taking steps to prevent it is a good idea.