the “benefits” in FWB

So it was one of those "oh my gosh, how are we so in sync?" kind of relationships. We'd started out as friends, went through a rocky beginning with his former ex declaring that she still loved him two weeks into the relationship, but we had so much in common that we were able to tackle that hurricane together. About a month ago I find out he wants to be friends with her again and then he starts pushing one-on-one time with her. I think it's a lack of respect and he thinks I don't trust him to the point that he can't continue being together. We met because we both bike. I had only biked with him twice either alone or in a group since Valentine's Day. A little more isolation because of all of this I thought was supposed to help ease the problem, but they've seen each other biking 4/5 days since we broke up and thanks to social media for cyclists, I see all of it. When we broke up, he gave me a pack of TP, a battery for my thermometer and some ramen. I kid you not. These are strange times.