You seem to be really over thinking. Having fantasies or thoughts of sexual interest in someone of the same sex occasionally is normal. No big deal. Nothing to obsess over. If you have no attraction for someone of the opposite sex, why force it? Maybe you are bi or gay. Wait it out doing nothing until it is more clear. Get a hobby, dive into school or work, better YOURSELF. And if you suffer anxiety, seek professional help be it counseling with a therapist or working with a psychiatrist. And if you continue to be confused about what sex you want to be with and struggle with, talk it out with a therapist. good luck
You say you lost your attraction to the opposite sex because of your phobia over being gay, and it's lasted for two years. Is that right? In your therapy, have you done any work on your bias against gay people? Most of us have it, it's been part of society for the last few centuries, and it's caused a lot of pain such as yours. If you lose your fear of being gay because you believe being gay would be a horrible thing perhaps your apparently completely heterosexual self will emerge again with desire back. Or you know, you could have talked yourself into a pretty bad depression, and depressed people often lose their sexual appetite (it's also a side effect for some on SSRIs). What you've got is a gigantic mental block, not OCD really, and somehow you've got to find a way to puncture that block and find your whole self again.