Your post is full of "I base my self-worth on what other people think."
Then you say "I feel like poly men are all about notches on bedposts" and follow with "I want to keep our relationship open for my sake but then when he starts dating ppl I get unstable w jealousy all over again".
So, basically, the problem is you. You are not happy with yourself and are allowing other people to control your life. You need to take control of your life and find peace within yourself.
However, there is no such thing as perfect happiness or completion. The human condition is such that change is the only constant, and we can choose to learn and grow from change or we can spend untold amounts of energy resisting changes.
To thine own self be true.