"lock your spouse in a box" , or "trust" THESE issues , comes after precautions , THEN if your wife cheat on you that her fault .
I mean you can't be partner to her fault then blame her alone or even be sorry .
for some reason in many cases (the overtrust) that turn to cuckold and cheating .
then If we give a space to your wife to cheat on you , could you blame her ?
I know this wasn't a question for me, but I feel it would indeed be his/her fault. It's personal responsibility. You don't have to have sex with other people, it's a choice. Even if there's the opposite sex in the same room, and you're both alone, you still make that decision. No one forces you to. So I think it's the person's responsibility.
All you can do is find a good partner and trust them. I can't control my husband's life, and likewise, he can't control mine. If someone cheats, of course the other person would be hurt but it's better to trust than being jealous and paranoid all the time, that's unhealthy. I'm not saying someone has to be 0% jealous, but if you're suspicious of your partner just because they go out, to me, that's too much.
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As for your original question (post #1), I don't know. I don't really have any ex and my husband only has one and he hasn't stayed in contact with her. If he had though, well I would be a little uncomfortable, given the circumstances... I don't think anyone would stay friends in such a case (I don't want to go into details).
Though I don't feel that being friends with an ex always means it's bad, like you still have romantic feelings for them. Sometimes people were friends before they were in a relationship, tried being a couple and found out it just doesn't work and would rather just be friends. They find out that they don't love each other in that manner.
Maybe that situation wouldn't bother me, as long as they didn't spend a lot of time together alone. I mean, I'm not perfect, I would get a little jealous then.