My boyfriend (M32) doesn't want me (F23) hanging out with friends?

Let me start by saying that I don't have many friends, just 3-4 ones and we're very close. We've been friends since high school and they're important to me. They are great people, so I really don't understand why he has a problem with them. He has only met two of them and said they were very nice, so I don't know what changed now and he doesn't even wanna hear about them. I barely see them to begin with, since they are all busy with their own lives, with college, relationships, jobs etc. We hang out maybe like twice a month if even that. But suddenly he doesn't like that. It doesn't make sense that he is jealous, because they are all girls and we rarely see each other anyways. But every time we do, he gets upset and almost annoyed in a way. I'm writing this now because one of the girls is in town and we made plans. He got upset and told me that I don't need friends because I have him and that should be more than enough? Like excuse me, what? I didn't want it to get worse, so I told him that he was welcome to join us, but he was still mad. He kept going on and on about stupid things and saying how I'm immature for hanging out with the girls and things like that. I'm sorry, but he also has guy friends and I never complained about them hanging out together.

I guess I just don't get it. They are great and very sweet. They never bothered him or anyone. And it's not like I spend more time with them than with him. Not at all. Now I've made plans with one of the girls this week and I already feel guilty.

We've been together for less than a year by the way and we don't live together.