Sex with an ex?....

What do you guys think about still having sex with an ex boyfriend (that's all it is) while talking and dating someone new? We've only had sex once since we broke up but I don't know. I'm on the fence about doing it again but honestly still want to have sex... Have any of you been in this position? 
Please don't judge either. Some of you can be really judge mental and that isn't needed. You can give your honest opinion but don't be rude. Thanks!