ex boyfriend/ fwb

Me and my ex boyfriend have been hooking up for the last 2 months and have been on and off for a year. But I'm worried that he is jealous that I had sex with someone else when we were taking a break and is hurt about it. He brings it up sometimes when we are together. I don't know whether it's because he is mad at me for "cheating" and me being with someone else or because he may still have feelings for me? It's all very confusing and hard because I still have feelings for him and I think he still has feelings for me due to the fact that we keep coming back to eachother after all of this time and can't really let go of eachother... I just need some advise on what to do or maybe some insight.:)