I've never really been attracted to girls, and I can remember sort of having crushes on boys in primary school. As with Gideon, I realised it as a sexual thing around puberty, and I came out to my friends about 3 years ago, and it was not a happy time for me. Everyone in school found out, and I was subject to a lot of homophobia throughout my GCSE years, but when I told my parents they were very supportive of me, as were my friends. I couldn't have got through it without them! About two and a half years ago, I met a very special person, and we've been together now for nearly 2 years and 4 months, and we both helped eachother through the troubles we had. Now I'm in 6th form I don't have much contact with the rest of the school, so the problems are pretty non existant now.
Generally speaking, family and friends may take a while to get over the revelation, but afterwards will be fine. The main thing you may want to consider is others in your environment who may cause problems. As far as I've heard, uni is the ideal time and place for coming out, whilst you may want to excercise caution if you're still at school.
I hope everything works out for you!