Bro, I really feel sorry for you. I have had this problem happen only once and it was actually with Chilli the WL that you really like but that was only because she reminded me of a workmate and it felt wrong to be doing that with a workmate. I hope that someone comes up with some good suggestions to help out.
Just like some therapy to overcome some phobia, try to do it with that real life work mate so as to cross that psychological barrier !