If you want to make it work, talk to him. Don't let the unspoken expectations in your relationship lead you to avoid the tough conversations. Confront him about the affair. Just because he cheated this time it does not mean he will do it again.
If he is willing to continue your relationship, shows remorse for the affair, wants to end it with the other woman and says he is committed to you, believe him. If he does it again, then you can question his integrity. And make your expectations clear. Your monogamy agreement is when you put all of your expectations out there, when everything is spoken out loud, and when you talk to one another before you cheat, not after.
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The point of a "new monogamy" is to make all of your expectations — and disappointments — explicit. If your relationship isn't everything you dreamed about right now, sit down and talk about it. Ask your partner to talk about how he feels and talk about your own feelings.
Has your relationship been fun and exciting or has it turned out to be less than stellar? Is it everything you have dreamed of or is it kind of a bummer? Now you are talking like a real, honest and monogamous couple. Monogamous couples talk about monogamy. They know that monogamy is a choice, every day. Some days are easier than others.
Some days you might even want to cheat, and some days it's not even a thought. Talking about it honestly could prevent a breakup. A "new monogamy" means actually discussing your fears and frustrations, and creating a new plan going forward.
Your partner might cheat again. But he might surprise you as well. Talk to each other and don't take advice from well-meaning friends or relatives. They aren't in your relationship, so they don't know what it's like for either of you.
Be a new kind of partner and start a new monogamy, with the partner you have. Before you end it, give this one a chance, if they want it. Don't assume an affair means it's over. Talk openly and give your relationship a chance. And if they show up late for dinner again, think carefully about your expectations, and remember you don't have to continue to let anyone disappointment you. And don't let your denial get the best of you, either. But do remember — next time, it might be you who misses the bus.
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