I have pretty much the same problem, except for swim team... If you want to be noticed as a girl, wear your hair down or something... but if you want to show off, don't try too hard so people won't think of you badly. The best thing you can do is be nice to your crush and talk to him.
If shes going to sleep with another woman how important could you really be to her? I mean seriously. If she was in love with you, not only could she not do that to you, but she shouldn't even want to if you really broke her heart. I think if shes already been with another girl you should move...