I don't want to "micro-manage" what you wrote, but they were engaged, not dating. There were also kids involved. Typically, the scenario they were in together would prompt a woman to be more "forgiving".
So we're clear, I disagree with this mentality, but it is what it is.
Like someone else said, I feel bad for the kids involved, and although he may have F'ed up some, I still hope he pulls through.