She has listened to what posters have said, otherwise she wouldn't have replied. No-one has any idea what she will or won't do. The tone of some of the posts is quite aggressive and nasty.
Unless you have been living in a cave, it is hardly likely to be the most extraordinary revelation of the century that a man might try to cheat on his partner.
This is essentially what this post is about. Her partner tried to cheat, she got suspicious and confronted him and they are now dealing with the fall-out.
I think that is what is going on.
Equally, unless you are living in, maybe, a society where non-monogamy is punishable by something like stoning, then, unfortunately, like death and taxes it is going to happen to somebody somewhere.
The poster sounds quite level headed actually which is more than can be said for some of the responders.
Of course we all aspire to have perfect relationships with kind, faithful, intelligent people who worship the ground that we walk on and wouldn't do anything to risk the relationship.
Sometimes things don't go that way.
"She's not a fool for not throwing him out immediately." That is a contemptuous comment which shows that you have not remotely considered their children in all this, or the fact that you cannot actually throw someone out of a house which they legally own. Are you a lawyer? You sound like a fool.