single w relationship problems πŸ™„

I'm single, but I deal with relationship problems... my fwb and I went back to be friends a little bit ago, and he still gets mad at me when I do single people stuff, like flirt with guys or get car rides and just car rides from them. What do I do and what do I say to him to make him understand in the nicest way possible that I shouldn't be dealing with relationship problems while I'm single πŸ˜•