[Lionheart]

Well I think the best thing to do is to talk to her.
Just make sure that she knows that while you like her you have no intention of being with her as long as she has a boyfriend and that it's troubeling for you if shes so touchy with you.
That way you can get this of your chest and she may also tone down on touching you and stuff so it might be easier for you to be around her without constantly having conflicting thoughts. She might also stop making these jokes. Afterall there is a chance she isn't even aware you like her and to her all of this is just a joke and she'll stop the second she knows its actually hurting you.
Nothing much you can do about the others but they might catch on that things have changed and automaticaly stopp teasing the two of you.