My fwb(28M) got mad after I (20F) slept with his brother by accident, now he wants to end things and I feel guilty

So I’m 20F, he’s 28M, and his my first fwb

I only smash with him and he smashed with bunch of girls( I didn’t ask him and judge him for that)

We started this back in October 2025. Everything was going fine until mid-January, when I suggested we set a regular schedule for hooking up. He got triggered for no reason and wanted to call it off. I said okay but then he immediately regretted it and said we could do it one last time. After that, he kept texting me and said he didn’t want it to be the last time, he wanted to see me more. I was so confused cuz he was the one who ended it.

Things went back to normal, and then in early March, his insta got banned for no reason(that was our only way to contact each other). He didn’t make a new acc, but I found his Reddit and texted him. He said sorry for not telling me cuz he had no way to reach me.

After we reunited, he said he missed me a lot. He asked if I’d seen with any other guys and why I hadn’t. He also asked why I didn’t come to him sooner. The vibe was kinda weird, like he was trying to control who I can see. Even before he lost his insta, he always wanted me to stay overnight at his place. If i couldn’t, he’d rather pick another day when i could. I’ve only ever been with him, and no one else.

Now, here’s the messy part. During the time he lost his insta, I randomly met his brother on insta( I didn’t know that it was his brother, they don’t live in the same city). His bro told me he was coming to my city and asked if we could meet up. And I said yes cuz he seemed chill. We went to a bar, and ended up having sex. I didn’t really want to but I didn’t know how to say no, and that’s on me.

The next day, my fwb came to me and said he’s pretty sure I fucked his brother and wants to end things. He says he’s not pissed or upset but his reaction clearly shows he cares. I feel really guilty now.

Is he getting jealous? Or is he catching feelings for me?