Confused

So my boyfriend and I recently broke up(about two weeks ago) and last night I went to hang out with an old coworker I've always had a crush on but we both were in a relationship and we ended up having sex. (He also broke up with his girlfriend around the same time as me and mine) 
But I'm really conflicted, I'm not sure what to do, everything was really good and we talked about nothing changing afterwards since it's something we've both always have wanted. But I can't help but feel slutty since my ex and I have been talking everyday since and want to work out stuff and eventually get back together. 
Overall can anyone give me some advice on what I should do?