Need some advice about my relationship...?

I feel so messed up! My bf and I had a huge fight over him sleeping over at another girls place after going out to the bar. She's a girl from work and I kinda liked her but not anymore....apparently she told him that night that she liked him at the bar... for some reason he didn't tell me this straight up, it was only after we argued that he told me. I felt hurt. He said nothing happend and I do believe him but it still bothers me! He just called to say he was going out for some food after work, naming a bunch of people including her room-mate-but not saying her. I asked if she was going and he said yes...I asked why he didn't say that...and of couse it was because he didn't want to upset me....am I upset?? Yeah I am. what is happening to us? He said he told her that they couldn't hang out anymore because it wasn't good for our relationship...he said he liked her, not that he would break up to be with her but that he liked her...****! how do I get over this?Need some advice about my relationship...?
Tell him to start being more honest with you. It's not right that he should be going over to other girl's places even if he doesn't do anything with them. It's disrespectful towards you. If he doesn't want to respect your feelings, then it is his loss. I hope that things get better for you.