Hi 1124girl,
I think this is an ethical question that every woman has to ask herself. There is no judgment on the choices; however, one must weight the consequences of her actions of carrying out that attraction. It's natural to have feelings that you rather not have towards another human being. However, our minds and hormones are very tricky things. I personally would suggest staying away emotionally even though you still have to see that person on a regular basis. Stay strong, and focus on people who are truly available and "good" for you. Forbidden love usually ends up hurting both parties, and even more people involved in the situation i.e. yours or his current partners, families, work...etc. I know it's difficult as attraction is attraction, and it is hard to be explained away by our logical mind.
I usually tell people to follow their heart. However, in this case, I would say to "think" through your decisions. I believe you will know what is right for you.
Take care,