Umm... I can "kinda" relate... there is a guy who teaches salsa classes at my dance studio who has kind of a reputation as a heartbreaker. One of my friends has a big crush on him. I though he was kind of swoony for a while but then I realized I had to just never spend any time with him because he was just a little too dangerous.
It sounds like avoiding this employee isn't an option for you... Maybe you can try a little harder to avoid him though... What about moving to a machine further from him... Or if he comes into the room, go to the weight room or something?
Or... if that sounds a little nuts... then just try not to let it take over your head. If you need a little "crush" to motivate you and you don't want it to be someone at the gym, what about a little photo of some good looking celebrity posted someone where you can look at...
Or... if it's not bothering you too much and just need some absolution... I really don't think there's anything to feel guilty about for having a crush, especially if it gets you into the gym