Do you trust your boyfriend that he won't be cheating on you? Do you know this girl well enough that she's not trying to steal your man? Have you ever joined them before?

If they're just good friends, I wouldn't mind at all. Guys don't like their girlfriends to get too jealous, they get annoyed Give him some space... he has his own life and you've yours too and a couple doesn't have to spend 24/7 together. I always hang out with my guy friend often (we work in the same company and we even live together) and my boyfriend doesn't mind that at all because he trusts me.