OMG WHAT IS GOING ON UGH !

So me and ex have been broken up for a year or 2 now not really keeping up but we've became best friend and we talk damn near everyday and every time we're together we always end up having sex we both still have feelings for each other but we're both are seeing other people I know it's wrong but it's like we can't leave each other alone and I'm confused what should I do ?