I can't stop ruminating obsessively about a guy I dated

A coworker introduced me to a guy and we hit it off great! (Which doesn't usually happen to me.) We had a ton of similar interests, we both had creative passions, he was funny and very sweet.

I have zero friends because I find it hard to get close to people, social anxiety (which has been getting much better) & not a lot of adults seem to share my interests in stuff like Disney movies, games, animation, reading, anime etc. So I was really excited about this.

Long story short, while I wanted to start as friends and take things slowly, he very much wanted a relationship and because he would send me the sweetest texts until like 3 in the morning, I decided to go along with it trusting him.

A few days and a couple dates later we have sex (which wasn't even that good haha) because I so strongly felt I could trust him due to him being a friend of my coworker and how well we connected. The texts slow down the next couple days and suddenly stop cold for days.

He ends up breaking up with me via text, apologizing profusely for what he did. He blamed it on his apparent depression, something about how he gives people high expectations of himself only to hurt them later and yada yada. I begged him to let me call him or talk to me in person, but he refused. Then my coworker tells me he never had feelings for me, she had to "force" him to be with me and that he had feelings for her. Then some drama for the next couple days due to her not showing any sympathy for my situation, for some reason she acted like the victim in this, him only texting me for her sake so I could forgive her as if I was attacking her or something (I just wasn't talking to her, but I told a couple coworkers what happened), etc. Fun stuff haha.

I was heart broken because he was supposed to be my first friend that I could trust and he broke it so hard within days. Now I've fallen into my usual habit of ruminating on it and I'm constantly beating myself up over possible mistakes I made that made him not like me, even though everybody tells me this situation was messed up and not my fault. No matter what I'm doing, I can't stop ruminating in the back of my mind.

Keep in mind I do have diagnosed ADHD, and apparently constant worrying is pretty common for those who have it. This isn't anything new for me, it's just a whole new level now in which I can't escape it no matter how hard I try to distract myself and it's getting in the way of things. I just bought a book off of Amazon that talks about obsessive thoughts & constant worrying, but I haven't gotten it yet. I can't afford therapy.

I wish I knew how I could find some friends at least, I think I need some to move on. At least to help me with my self-confidence. Or something, I don't know. Any advice on how I can get past this and move on?