Are friends really just friends?

So most of my girlfriends best friends are guys. What I want to know is, is it wrong for me to get jealous of these guys sometimes? She goes to there house, she goes to the bar with them, she goes to their parties and at first I tried to brush it off but lately it has been bothering me more and more. I see pictures of her with other guys on facebook and she says "Oh that's my good buddy from elamentry school." And they don't see each other that way. We've gotten in fights about it before and she says she'll stop hanging out with them if I really want that but I don't think I want to be that kind of boyfriend that make his girl stop seeing her friends right?