Infidelity would not have to be a deal breaker if it is merely physical. If a man says, "I'm sorry. I don't know what I was thinking. I love you. I want our family. I want to be with you for the rest of my life" - that would be forgiveable to me. If he LOVES the other woman, however, and is constantly thinking about her and holds her above his wife; it's a bit irretrivable I would think. Emotional infidelity is the worse kind. It can be ongoing before there ever is a physical relationship. If the husband has fallen in love with another woman, it's an ALMOST impossible hurdle to overcome. That kind of infidelity can be disasterous. And if there are children involved it's tragic.