As a 30 year old gay man that is still in the closet, I can definitely feel for you in regards to coming out. I struggled through my teens and 20s with how I really felt, am I straight/gay/bi/, etc. I did have girlfriends in the past, and they did not do it for me. I was dating a guy, and that has helped me to be able to accept myself more as a gay man, and through him, met quite a few friends that are making my courage to come out grow more and more each day. Some may say that being in the closet is living a lie, but that to me just sounds as though they don't know half the issues GLBT people face with their alternative lifestyle.
What I am preparing for is the acceptace / loss when I do come out. I have my plans of doing so that are slowly coming in place, and I plan to tell alot of people at once (friends and family). I am mentally preparing for the consequences that can arise.
The one thing I can say is, when the time is right, you will know it, and once everything is said and done, I am sure you will feel much better about everything.