It’s not your fault. Not at all. Cheating is an issue with the person who has cheated, never their partner. In all but the most extreme of cases, just leaving their partner is an option. So many try to justify themselves with some rubbish about their bad relationship. But many people have bad periods in a relationship, and most of those people don’t cheat.

People cheat for complicated reasons. I think they can be split into two categories: “good” cheater and “bad” cheaters. Bad cheaters will cheat over and over again, swear blind they’re doing nothing wrong and perhaps even gaslight you into thinking you’re the issue. “Good” cheaters don’t want to hurt you. God knows why they do it, maybe their parents did and there is some internal propensity towards that behaviour, no matter how much they agree with it. But good cheaters will feel guilty and fight hard to change and patch up some of the damage they’ve done.

Not all cheaters are bad people, but all cheaters only have themselves to blame.