I'm sorry, Dagny, but I cannot understand this situation at all. I couldn't from the beginning.
You used to think that he was a wonderful boyfriend, whom you intended to marry.
It's as if he wants you and doesn't want you at the same time. He wants you to be his friend, his girlfriend, his fiancee, his wife, etc, but he also wants to date others and he doesn't seem to treat your views with respect.
I'm confused by this.
I would simply suggest that you heed your gut reaction.
