My boyfriend is REEEEAAAAAALLY close to a girl, and it makes me uncomfy, what should I do?

Okay, so I have a boyfriend. He has this friend I mentioned. She's a girl; he says she's like a sister to him. My brothers (and me and my bros are uber close like relationship wise and we tell each other stuff) are not like THAT with me. By that I mean: he hugs her really closely and tightly and stuff like that. But I can't tell him, it's just hard to bring up bad stuff around him. I'm too happy. And I he says he loves me and I KNOW he means it, but it's still saddening to see them. Like, their one of those best friend couples who (if I wasn't already his gf) you'd say they're going to end up being together. :( they're just so cute!!!! But I know he'd not like it if I were like that with one of my guy friends. He'd probably think I'm cheating on him if I did that. I'm too loyal to him that it makes me sick thinking of doing that to him. But.... Yeah :( what should I do?