How do I stop being jealous for my ex who wants an open relationship?

So, I got jealous in the past when my exes would be messaging other women, ngl my intuition was right, they were cheating. I'm still in love with my ex and he still wants me but he wants to be in a relationship with me and another girl too. I don't know how to not be sick in the stomach and go along with it. I don't want to hear about self-worth, I've always been cheated on, I figure it's the universes way of beating jealousy out of me. He never talks about her, but she knows all about me and I've never seen her he won't even give me a basic first name so how am I to agree with something I don't know all the details? I love him with everything I have and I'll do it if it makes him happy. She seemed to just accept it right out of the gate because she'd shared her man before I guess. Makes me feel like she's cooler and better than me for being okay with it. Anyways, how do i not get jealous?

How do I stop being jealous for my ex who wants an open relationship?
Post Opinion