What I got from your first post is that he dismisses your feelings, accuses you of cramping his style and tells you you,re boring and disgusting (or makes you feel like you are). If you don't fee loved and appreciated you can NOT be happy with poly (and I wouldn't think you could be happy with mono either).
If he wants to have several relationships, he should work on making this one work. Making you feel worthless and like a failure is not the way to go. I think you need a lot of comfort and reassurance if you ever do end up in a mono/poly relationship (and even if you don't, considering your backstory, it seems you could use a self-esteem boost).
I would work on that first. You need to make sure you will remain a priority after you open your relationship, if you ever do. Problem is, it already seems like you're not a priority NOW...
I can relate to his feelings to some extent (I felt really trapped when I was in a mono relationship with my husband) but he needs to understand that you can't feel comfortable with it if he keeps sending a message that sounds a lot like "you suck, I want someone else", whether he wants it to sound that way or not.
Me: 31F, straight
Seamus: My husband, 32M, straight
Dragon: My boyfriend, 29M, pansexual, married to Fox
Fox: My boyfriend, 29M, homoflexible, married to Dragon