Ok fwb or boyfriend is mad cause I slept with another?

Ok my ex boyfriend came to town to visit for a week. So after he came down he called me and asked could we see each others bf he leave. I got to admit I still somewhat like him so I said yes. Ok i have a guy friend he's nice sometimes but sometimes he treat me so wrong like argue with me over stupid stuff, but later we always find ourselves in bed again. So anyway I met my ex and I got to admit it was nice so I told my friend guy and he was so upset that he stop speaking to me for 2 days. But tonight I hook up with my fwb or boyfriend and he kept asking me about the other guy. He looked so sad when we were together I can't shake that off. Like if we kiss he would asked is that's how I kissed him and so on. I feel really bad cause I do have feelings for my fwb which he have also feelings for me too. But that's the thing I feel like I was so wrong to do that