I think you will find that the RAF is quite accepting, and most of the younger generation will not find your sexuality an issue.
I know three gay pilots in the RAF, and one in the Navy. All are open with their sexuality, lead a normal life and let the Flying do the talking. As long as you are happy to be one of the lads and enjoy some banter, and do your job well then its really no problem. The current generation of Pilots and aircrew will be supportive of you provided you don't use your sexuality as an excuse or a barrier to being a team player.
You will get biggots and idiots in any walk of life, and you have already heard their outdated ramblings. I guarantee that if you show that you are a superb Officer and Pilot, no one will stand in your way, and you can have a fantastic life in the RAF.
Be yourself, and if the RAF is not for you you can always fly Navy!