The other posts offer some good perspectives.
The sexual aspect might be a place you could benefit from the insights of a good therapist? It sounds like there are unresolved traumas there which might be causing you pain and anxiety. An internet forum isn't the place to talk about those, but therapy is.
Personal growth is beautiful, and new relationships can be a wonderful catalyst for growth. But a person can't grow in a particular direction until they're ready -- it will only happen when it can happen. When the psychological path becomes open.
I'm a little concerned because what you write seems to carry lots of anxiety and dread associated with being sexually active. I might guess that if you force yourself into poly relationships without addressing that -- without opening the psychological path -- then you will have to suppress your fears and eventually they'll burst out in some potentially frightening and destructive way.
That's just guesswork on my part! I ain't no psychologist. Talk to a professional about this if you can. (Maybe you already have?) The right person can give you great insights into what is going on in your mind.