Forgiving yourself when you were the problem

How do you forgive yourself when you were the problem in the relationship? 

My ex is nonmonogamous and had several other romantic partners when we first started dating. She was upfront about this, told me that this is how it’s going to be if I date her, and never lied or deceived me when it came to spending time/dates with her other partners. 

I didn’t know this at the time, but it turns out I am extremely anxiously attached when it comes to romantic relationships. Choosing to date a nonmonogamous person was the worst thing I could’ve done to myself, and by the end it completely broke me as a person. I tried so hard to be okay with it and make it work; I read the books, listened to podcasts, scrolled the reddit threads, ect etc. but ultimately my jealously and insecurity got so bad that I started having these emotional breakdowns and fits of jealous rage that led to her breaking up with me. 

I know it seems like it’s for the best that this relationship is over, and there’s a logical part of me that knows that. But the fact remains that I was/am still truly in love with this person and not only is the breakup extremely painful, but I can’t stop feeling ashamed for the way I acted towards her during my emotional outbursts. I used to be a more secure person when I met her, but the toll that all the jealously/insecurity had on my nervous system had eventually reduced me to a clingy, hypersensitive, crying mess of a person. She became completely turned-off by this behavior and dumped me, and I can’t really blame her for it. 

I’m still picking up the pieces, but I guess what I’m trying to say is that it’s hard to get over a break-up when the other person didn’t do anything wrong, that I was the one that made the mistake of getting attached to a NM person and I am the one paying the price for it now. While she, of course, has other partners she can turn to for comfort and emotional support. 

I just want to be able to forgive myself and stop feeling ashamed for the way I acted (jealous, insecure, etc), because I feel that it’s preventing me from letting go and moving on from this experience.