Hmmm? what should I do?

well there is this girl that I like a lot, and I'm quite sure she likes me back, and she is having a party on saturday. However, she is also friends with a guy that likes her, and he is going too. I don't know if she likes him, but she says they are friends. They both have the same cles together, but I don't see either of them except lunch and recess. I'm scared he might move in and steal her from me, and I also think the party will be uncomfortable with him there, what should I do?