Would you be ok with your boyfriend hanging out with girls he knew from back in the day?

The girl connected with him on facebook, and he just moved up to Colorado which is where she is living. He doensn't know anybody up there yet. She herself is in a long distance relationship. But yesterday I called him and he told me he was heading to a Rodeo to hangout with her. They were there with other people but he stayed there till 12am. When your in a serious relationship w/ someone for 2 1/2 years, don't you feel its innapropriate to just have these kind of get togethers with girls? We talked about yesterday, and he seems to think that it is ok to hangout with females, or anyone that he knew in the past, as long as he is telling me about it, there should be no problems, but i'm not ok with it. I hungout with a guy friend of mine early on in our relationship and he didn't like it, and felt it was innapropriate, yet all of a sudden its appropriate for him, just because he's in a new state with nothing to do until he starts work. What should I do?