Feeling insecure about my boyfriend's new female friends?

Anonymous
We've been going out 3 years and this year started working and he started another course in uni. He's always been very outgoing and had lots of friends, but mostly guys who I know quite well.

But since starting his new course he's making a lot more female friends. I've met most of them at least once and some are very nice, but a few of his closer friends aren't that friendly toward me and I've started to feel very insecure about him going out with them and staying overnight for parties. I've brought it up a few times and he says I'll like them once I get to know them and he'd never do anything that would hurt me. I trust him but the fact I'm worried that one or two of them like him, and I don't like not being there. Plus I don't get invited out with those particular girls so I can't get to know them. I just want to stop feeling so insecure and relax about it, but I don't know how?
Feeling insecure about my boyfriend's new female friends?
7 Opinion