Count me as one who doesn't think that just because a guy has fooled around or did some experimentation means they are automatically gay or bi. I suspected I was gay when I was in school because I had zero interest in dating a woman but I was very afraid to admit it to myself due to my religious upbringing and living in a small community.
After I had sex with a guy for the first time at 26 I got a therapist and he and I worked through my guilt, shame, and he also educated me a great deal on sexuality. There has been a significant amount of research in the fields of biology and psychology to determine why people are gay and to be honest I think it's kind of a waste of time. Science still doesn't conclusively know why some men are sexually attracted to males even though there has been some interesting ideas.
Granted I live in a large city and realize there are still plenty of people around who are against homosexuality but the general stigma around same sex relationships has largely faded.