Dear Marcelio,
Fantasies, what you think about while masturbating, can be totally outside what your sexuality normally includes. This is totally normal. So while you might enjoy imagining gay sex while you masturbate, it does not mean that you are gay, or want to act on the fantasies.
There are many fantasies that people have that they enjoy in their mind, but would never want to physically act upon. (Lesbian sex or domination, for example, is something people might fantasize about, but not want to actually participate in.)
As long as you’re not hurting yourself, or others, enjoy your fantasies!
Have fun!
Team AlterHeros