lol! I don't think dutasteride can make u gay. You may possibly be gay already and thats why your worried something may tip you over the edge. Best bet is to get a picture of brad pit, and one of jessica alba. Then decide which one your gonna use as wanking material. If you choose to tug yer todger to Brad Pitt then i'm afraid there's a possibility you may be gay.
Anyway apart from potentialy turning you gay, the main side effects I am worrying about are the reduction of DHT in the brain and other things like permenant reduction in sperm count etc.