Since FML still doesn't let us comment or read replies to an OP's follow up, I'll leave a reply under your comment OP. You seem to be doing a lot for a man who lied to you and his potential mistress. Keeping him on a short leash, monitoring him like a child, is that really what you want to do for the rest of your life? Do you want to be second guessing yourself whenever he goes to work or for a swim? Seems like a hard life to life to live. Secondly, the woman is the one that decided to walk away according to your comment. He would have kept this shit going if she was okay with destroying a relationship.

If they didn't do anything, why is this under love and intimate? I wouldn't let him invite that woman over anymore if he's just going to lie to you.

OP, I was in an open relationship too and he became even more selfish over time. If he did that and used your past open status as an excuse, he will find a way to do it again.

so why are you worrying about it?

... their are plenty of guys out there who will love you way better than this asshole. no offense but just leave him. its not worth the heartache that is to come. wtf are you monitoring them for anyways? tell that girl she's not welcome in your house anymore and if you catch them again tell her lover and dump him for good. since you probably don't want to leave him.

I’m sorry, OP, but are you insane? You’re still going to marry him after he’s proven that he can’t be trusted? Good luck. You’ll need it.

So you wake up at 1am, he's in the pool with a topless woman, and you believe that nothing happened because she values her relationship? You really believe that? Even if she didn't continue because of her relationship, which I doubt, he still had the intention. Marry him only if you're prepared for him to treat your relationship as open.

OP, you need to end this toxic relationship. he's not worth the effort and it's only going to hurt you in the end. Cut him loose.