Help! Opinions!

Help me with your two cents please help! My coworker and i flirt sometimes, kinda, and shes from a fam that is open to bisexuality and gay sexuality and mine isnt for the most part! Shes beautiful and i cant see myself doing sex things with women but groups like this and my history of having strong one on one female relationships suggests to me i am at least very much in need of the strong emotional ties with women as relationships in my life! And she is the only person who we both discussed the idea of being intimate with, except i decided i would not want that (esp since she is ENGAGED to a DUDE). Anyways, she sometimes smacks my butt whenever she first sees me and i get embarrassed because other people see and i dont want to be seen by others in that scenario ina work setting! Its a casual work setting.very very casual, but i feel uncomfortable! As i type this i feel i should tell her outside of the initial moment so she finally gets that its not ok. In the beginning it was extremely flattering. But i would never let a dude do that! And since then, i feel like i am repwating myself and shes not respecting my boundaries. BIG NO NO. but i like her to much as a friend! ... Help and thank you! I appreciate your ideas and help!