If it is annoying you just have a word with your boyfriend about it,just be calm about it but express your feelings.
My husband had some friends that were interested in more than friendship as well. As we got serious, they drifted out of the picture. It is really your boyfriend's responsibility to set the tone of how things go with his female friends. If he has no feelings for her, he should speak it and act that way (romantic ones that is).
Beward of the guy that needs the secondary gain . . .which means that this friend that has deep feelings for him somehow feeds his ego even though he doesn't return the feelings. He likes that she likes him on some level or he'll stop her from acting "cute" as you say.
good luck
It sounds like you're all pretty young. She feels affectionate, he probably does not mind it, and you can't hint him into quitting. If he were your husband, in your shoes I would tell him that it would be very nice of him to back away from her when she touches him, or I would just arrange your lives so you are not in situations where she will be. Given that you are not (and please don't tell me you have to be the places where she is, drunk), I'd just get under his arm when she's around, and snuggle up to him with your arm around him. She will probably notice that you are there when she tries to lean on him. Don't confront her, it will just make you look small.
Frankly, the best idea is not to be around her when she's drinking. The younger you are, the better this advice is, since up to 18 teenagers shouldn't be drinking anyway.