Is poly right for you?
I respect your efforts to be comfortable with something like poly, but from all your posts...it really doesn't seem like poly is a match for you.
Yes, there are struggles, but if you have "severe" reactions to poly, jealousy that overwhelms you, worries that your girlfriend will kick you to the curb if YOU get a girlfriend, too....it just doesn't seem like a healthy environment to begin new relationships.
Balancing multiple relationships can be tricky, but, from personal experience, I can say that poly makes me happier, more relaxed, and more myself. It's not something I forced myself to tolerate.
If that doesn't hold true for you, it's perfectly okay to be monogamous.