even I'm straightforward monogamous myself, I personally think that there are people who view this thing other way. Nothing wrong it in IMHO, if you are yourself fine and "balanced" with that thing.
At this point, I'd absolutely not to get married with that man. I think that maybe the most logical thing would be to run away, but however, I wonder if there are something wrong with your man, which he then "unloads" by being disrespectful toward you? If so, he needs help + new coping strategies as well and the thing could work out if he received help for his own situation first
. But this means that he truly has to want
that help himself
and it's never OK to pour your own problems to someone else's neck
, especially if she carries wounds like you've from your own childhood.
However, continuing with a partner like him would mean taking a risk. There are people with psychopathic and narcissistic or plainly just less admirable traits out there and the risk of getting into their 'games' after they have received "help" is, still, there. Never been there myself but what I've learnt from others and as a part of my studies (I'm a bachelor of social services), people like start slowly; at first they treat you like a queen, then small things sneak in, such as a little dig here and there, then maybe more serious name calling or other mental abuse, then they perhaps start to throw things or show other physically aggressive symptoms, perhaps isolating from your friends and family and finally they'll hit you. OP, I absolutely don't mean
that your fiance is like this, maybe it's something smaller bothering him (and it'd be worked out for example with the said professional help given to him & accepted by him) but I'd stay alerted and check these things once a while if you feel that there is something 'wrong' with him. Especially if I had a background like you have, I'd surround myself with 'safe' people.
As others said, maybe the polyamory thing bothers him, perhaps it's something else. I think that openly polyamorous people or monogamous people who are ready to accept that their partner is polyamorous are probably still a minority (but they do exist!), and you need a person like this so you can have a balanced relationship if you polyamory is your way to go. Some monogamous people can perhaps accept it after processing the thing first theirselves or in couple counselling but some will never do and it's something that we just have to accept.
You are from US, right? As coming from Finland, I don't know how things work over there but if there is even a small change to get any free/low-cost therapy or any kind of counselling, I'd try it. My childhood wasn't very easy either, and my therapist has helped me enormously. Depending a little on your therapy/counselling/help, you can perhaps also talk about issues like your life plans (like fiances and weddings and your worries related to them) with your therapist/counselor and will get some 'mirror' and fresh point of views for your situation from him or her.
Summarum summarum: I know that this man is important to you, you have common past and he has helped you a lot, but I don't think that marriage is the right & wise movement for you to choose at this point. As I described above, maybe the breakup or at least putting everything 'on hold' would be the best choice until you can figure yourself and the situation out or at least calm this all down a little. I also promise that there are men who treat you well and respect you out there, since I'm married to one of them. Plus, I'd say - even to the most balanced/problem-free people/couple - if you hesitate getting married to the point in which you end up to ask yourself the question "do I?", the time, situation or something isn't right for the marriage just now and if I was there, I wouldn't get married at that point.
And the last words - good luck and Happy New Year! I hope that this year will be a good one for you