My married but separated co-worker

I started seeing my married but seperated co-worker a year and a half ago.  At first it was innocent lunch dates with a little kissing then I noticed the ring on his other hand.  He told me he was married but seperated.  I decided to let him go.  Well, a few months later he approached me again this time the lunch dates became sexual.  I was sucking his dick, he was eating my pussy, he was sucking my tits, and then we starting having sex at the job.  I must admit I secretly fell in love with him.  Well I noticed he never wanted to see me after work hours and never called me either.  I had sex with him about 4 times on the job and then decided to end it.  I felt he only wanted me at work and that was it.  Well since the break-up we don't speak.  It's hard not to speak to him because I still have feelings for him, but I felt like he was just using me.  What should a woman like me do and how do I fight these feelings I have for him by having to see him everyday.  I've moved on from him but I miss the on the job sex that was the best time of my life.  I miss him so much.  What should I do?