Every relationship has different boundaries. I some cheating is the physical act of sex and in others there can be more emotional aspects involved.

The fact that you told him about your discomfort and him brushing it off is not necessarily healthy. It’s also disturbing that he never mentioned being married after all that time.

I’m not a part of this relationship but from what you have presented us with I would say he crossed a major line.

I’m like you where I give my boyfriend the benefit of the doubt. I think it can be difficult being in such a serious relationship at a young age. It isn’t realistic to think one’s partner or yourself will never flirt with someone. But there is a line and both parties need to know what it is. This woman clearly does not see the boundary of their friendship by completely ignoring the both of you when you were together and then running off with him and making physical contact as soon as you separate.

It feels like she is acting as though she has some type of ownership over him or a relationship that is more important than the one you have together.

If you are comfortable with them staying friends I would make the stipulation that he has a conversation with her about what is appropriate in their friendship.

If you trust your husband there are ways to work through this without cutting anyone out. That being said, you are not obligated to trust him. If he has already crossed a boundary you are not comfortable with you have every right to feel that way.

Personally, I would not be okay with this relationship he had with her. I’m not one for ultimatums, but in this case I might institute one. That in addition to having a conversation about what is appropriate for are relationship in the future so that something like this can be avoided. Unfortunately, the dynamics of their friendship may have already been established and it seems like a line has been crossed. I’m not sure how easy it is to change that at this point.