How i became a cuck [M19] (back then)

I was 19, working in fast food during the summer. There I met this really talk girl, very shy but she liked being talked to. And we talked, eventually we went out and became a couple. I kind of adopted her in a sense. In school she had been bullied and didn't have many friends. I helped her, she wanted to be an actress so I supported her. She signed up for theatre classes, became more and more confident. In not even 2 years she was a completely different person.
She had many new friends, mostly from theatre.

One day she went to some event in another city. Something normal. What wasn't normal is that she stopped uploading on her Instagram stories. Very weird, fortunately her profile was public so I looked it up anonymously and indeed, she had blocked my account from seeing her stories. In one of the stories she was hugging and dancing with a guy from theatre, caption saying "we gotta play lovers again". I confronted her about it, and everything worked out well in the end.

Many months later some guy wrote to me, saying he had been fucking my girlfriend, telling me because they had a fallout and wanted to fuck her over. I didn't confront her as I wasn't sure if it was true. One day, when I left her home, I left my old phone there hidden, voice recording. I picked it up 2 days later and after hours of scrolling through the recording, I listened to her have sex. I was destroyed but something in me found it so hot and crazily, I jerked off to it multiple times.

I never confronted her about it and in the months we stayed together after, every time she went out somewhere or when she was busy I was having the craziest goon sessions as I was almost certain she was fucking behind my back. I had 3 girlfriends after, none were interested in the lifestyle until I met my current one who's already had sex with 4 guys since we've been together, I love her, she's fantastic.