FWB...with my ex?!

Is it wrong to have a FWB with my ex boyfriend? We had dated for 7 months about 5 years ago and now are friends, but lately every time we hang out we go at it without even intending to. I am talking to a few other guys as well and am looking for a serious relationship. I feel having a FWB isn’t the best thing right now but we both like the same stuff in bed and he’s respectful. At the same time, I’m talking to another guy who wants to give me the world but he lives a few states away. Thoughts?