How do I 28M stop retroactive jealousy from ruining my relationship with my fiancé 29F?

I suffer from retroactive jealousy (jealousy of partners romantic/sexual past) and it’s tearing us apart. Let me start by saying that my fiancé is amazing. She is funny, smart, kind, drop dead GORGEOUS, and extremely passionate about life. Before my retroactive jealousy, it was the most healthy and fulfilling relationship I’ve ever had.

About a 2 months ago, I spiraled and went through her phone and found some information about her past. This caused me to snoop more and ask for more information. While I knew she had a past and was a bit uncomfortable with those details already, this number which was simply higher than expected (30) and has caused me to have some terrible anxiety and ROCD. I have since been plagued with intrusive thoughts about the details of her history, feelings of disgust, and other emotions that I just can’t seem to escape. I have been going to therapy for 3 weeks now and started Zoloft right before this happened for other anxiety related issues.

I want to stay with my fiancé. I love her to death and I realize my issues are my own and I don’t logically judge her for having a past before me that has never once affected our relationship now. I also have a had partners (14) and it would be so hypocritical for me to judge based on that alone. I truthfully wouldn’t even second guess anyone else in the world having that amount of sexual partners other than my fiancé. However, the intrusive thoughts and anxiety have made me feel like a shell of myself. I have severe episodes of anxiety and she obviously knows the situation. This has caused her to feel some shame and frustration and it’s driven us further and further apart. I also now (and have always somewhat) struggled with sex because I tie so much of my own value and get validation from sex due to some trauma from a past relationship. I really just am looking for some advice on how to maintain my relationship and my feelings towards my fiancé until I rebuild my confidence and self esteem. I hate this for us and have considered all options but I know what I truly want is her.

TLDR:
Retroactive jealous of my fiancés romantic and sexual past is tearing apart my relationship. How can I rebuild/maintain my relationship while I work through these struggles?