Just don't know how to do this...

So there's this girl, we've been spending a lot of time together lately (as we are in the same circle of friends), but for whatever reason it has always been with our other friends there, so it's not as if we have been out on a date or anything like that.

Anyway, I really think I'm falling for her, now in any other situation I would have just come right out and just asked her out on a date. However, the other night we we in the pub with friends and the subject of boy/girlfriends came up, I get the impression that she has one (in her home country, as she is an international student) but she didn't actually say so. At one point one of my guys friends said something like "ahh I have a girlfriend but I'm not happy at uni...", then I said to him jokingly, with her present, "oh she has a boyfriend and she's happy at uni." She just replied saying "i'm happy", so not exactly confirming if she has a boyfriend.

Then after a night out clubbing we stayed over at a friends place in his lounge and we just talked and talked for hours, so I think she likes me (she also makes references to me being buff and is quite touchy...), we also text quite a bit, but i just don't know how to approach this? Any advice would be great. Thank you!

Thank you for the advice guys. I think I will just approach the situation directly and ask her out, but I'm still a bit scared it will jeopardise our friendship if she then turns out to have a boyfriend/reject me..
Anyone managed to maintain a friendship after being turned down?