I can't stop thinking about my co-worker
Don't you know that she is married?
Yes but it turns me on ever more.
Attraction can be complicated but it is better not to obsess with somebody that is married and unavailable. It will just make you upset that you can't have her and you will keep thinking about her all the time.
I can't help it and she knows that. She likes the attention.
She could be leading you on and using you for your affection. If you keep obsessing over her, it will start to drive you mad. You should let her go and find another person to fall in love with.