Can someone be gay for years and then turn straight?

My friend has been in gay relationships for ages and not had any hang-ups about it, or phobia directed against him. Now, however, he really wants to be with a woman, and thinks he might just have this deep fear of being intimate with one, and if he can get over the fear then he will be able to be with a woman. Is he deluding himself or is it possible to change just like that?