Infidelity is a serious problem. When you are trying to get good done, but there are precious few people even with the desire against everyone else, you have to maximize all your power situations. One of those is the married relationship. But sometimes politics and prevailing views lead us to choose not so well causing situations for other better choices that make doing better in the future harder to do.
Mom and Dad knew that Dimetri would come with Vladamir, and that was fine, except for his wife. Mom never liked her. But this time no one believes old threats, so when the original wife said she wasnt a woman and couldnt be married to one of us if she was Mom took advantage of another situation to get Dimitri with the woman he always cheats with anyway, because the kids from those unions had always been too good for the mafias but there anyway as there is little else for a bastard to do any time. She was hoping there was something more to it than the kids but thats up to you, and if it doesnt happen this time maybe next time.
Conditions for the right kind of bond to form arent uniform but they always seem to involve a certain act. Its usually done in childhood, or premanhood as manhood can set on very late at a time when no one would ever think of him as a child, but there is a condition of thinking that has to be met before manhood is really there. Mom and Dad arent saying that there arent other ways to do it, but just that everyone who they have seen so far did it that way.
Whatever it is, it only happens when the woman is dedicated, and the man realizes that whatever he is going to do the best, he has to do with her, while at the same time being willing to go do that in a way that means frequent separation. Or another way to think about it is when you realize what you mean to eachother, what your relationship means to the world, and that you have to do those things no matter what.
I dont know this doesnt quite paint it, but I think it will help you feel more confident when you hit it.
I advise against avoiding it though, as that does bad things to people.