Should I be worried about my girlfriends male friend?

[Joseph]

I've been going out with my girlfriend for about 3 months now and i really love her and i think she really loves me but the problem is she has this male friend (NOT best friend) that she's always talking to. He's an okay guy and i wasn't too worried at first but one of her friends (also my friend) told me that my girlfriend would go out with this guy if she wasn't going out with me. This upset me but i let it pass. He's in quite a few of her lessons (I'm not) and apparently sits next to her in all of them. They're always talking on facebook etc and sometimes I'm talking to her, he comes along and they start talking and ignore me. As well as this she's always liking his profile picture and likes bringing him into conversations.

I don't no whether I'm being paranoid its just something I'm worried about. (He's single by the way)

Thanks!