How should I handle my boyfriend wanting to hang out with another girl?

My boyfriend and I have been dating for three years and he never hangs out with other girls. He just does not have that many friends that are girls. I trust him fully and know he loves me. His old female friend from High School recently asked him to have a "gaming" day which I assume means they will be playing video games. He used to like her, years ago but she never felt the same way. She has a boyfriend. I feel slightly jealous and he knows that. I want to let it go and encourage him to have a good relationship with this girl but I am concered that he will confind in her and honestly, that's my job. They have had gaming days before we started dating. I don't know what the best way to handle this would be. However, I know that I am definately not going to tell him "no", he is an adult and he can make his own choices and be responsible. I trust him. Help?

Ask yourself, if you "trust him," why are you posting this question?

It's understandable that he would want to visit his old friend but what's not understandable is why you and her boyfriend aren't included. That's the way adults do business even if it's playing games.

The smartest thing you can do is find something else to do that day. Maybe if her boyfriend has nothing to do, he'd like to come along. After all, you have as much right to "Gaming Day" as your boyfriend does.