Your dick does not know if you are gay or straight does it? Sexual physical maturity and all the sexual feelings before puberty are based soley around the genitals and you learn to stimulate those in a variety of ways with very little regard to your sexual orientation, when you first begin that voyage of discovery.
Of course you hear that people 'know' they were gay at a very young age. However, the discovery that you can stimulate yourself to pleasurable feelings (remember the ropes in gym class, girls?) were all consuming at the time and I think most of us had our favoured choices of masturbation long before we decided on our sexual orientation.
Those fantasies of who we want to stimulate our genitals, did grow as we matured but this fantasy, in my opinion comes after we learn to first stimulate ourselves. I think most people were in a state of shock when they experienced their first orgasm and thought of nothing else other than to keep on repeating the experience! This was almost always by masturbation and not thinking about another human being doing it to us because yes, we did think we were the only ones this was happening to! I don't think the average masturbator mentioned that in show and tell!
Only the individual can know the way they like masturbating and how their genitals feel in response to this touch. This does not mean you cant be taught new tricks. We should know ourselves intimately and how we bring ourselves to climax so that we can use these techniques WITH other people and see their reaction - and vice versa.
As for guilt - get over it! It's natural and the essence of life. Without a sex drive mankind would die out!