How would you cope the best way?

In my past my partner tried to hide from me his ex wanted him back to a ridiculous great of length but I found out anyhows and when I did it had gone by a ridiculous amount of time, which he had during, self inflicted, built up anxiety. I let him off the hook as by the end of the day I came to the conclusion he hadn't cheated. Before lots of things did not make sense and I could tell something was wrong by how others acted and you just go into this mood when you think you're crazy when all along you're not. Adding early on I got the notion I was not the only one into him, there was particurly someone else but she pretended to just be his friend or part of the group. I saw this coming but can not remember it made me too effected by it, could be because it was still so early on. I guess I thought with time if we proceed, would be serious my socalled rival would get the picture and stop trying. Like his ex she escalated her game as she felt she was loosing, or had nothing left to loose, but right before that I had enough of the pretending game and told him this got to stop if he was serious about me. Time passed which during as a result from anxiety he has become jealous of me. I did not get it was as bad as it was, the cycles. Now he has befriended someone. Female, who too has her mental stuff. And my whole system is reacting, Im sad, angry, to be calm again, etc. We've been apart on my request but are now with some of his ideas going to see how this goes. I feel she could be anyone. She is not the one who made a commitment to me, know our rules. I have never confronted his ex or the friend rival as well and am not about to break this tradition. There could be a 100 of them, it's how he is. How do I keep my head as cold as I after all managed to do before? I am in some waiting mode, I can't describe, but don't like that, is there something you can do, think, to change it that would be better for me?

How would you cope the best way?
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