Am I bisexual?

This is a two-part question.First, I am a 21 year old guy and unquestionably heterosexual. I have no desire to pursue intimate relationships with other men and honestly only ever consider it when I'm horny. I masturbate to gay porn sometimes but I usually feel guilty afterwards and not because of social conditioning but because it feels inauthentic to who I am.However, when I am horny, I do really get off to it and enjoy it. I fantasize quite a bit about gay sex and sometimes do really consider exploring that, but then the feeling goes away and I think about how it's not really something I want, and I'd rather not discover I'm not into it while in the process of experiencing it, you feel?The second part of this question is that I am constantly worried that people assume I am gay because I haven't had a relationship with a woman, and used to do things more typically associated with the gay community, such as musical theatre. Two of my all time closest friends were also gay. I have also been known to be highly sensitive and artistic, and just unlike typical guys my age or even my brother and cousins.Again, I really don't have an issue with that itself, and I feel like if I was actually gay I'd be open about it, but it's more the fact that people are assuming something that is inaccurate and it upsets me.The weird thing about that is it's almost like a negative feedback loop. I feel like if I have to keep saying in my head that I'm straight, that's proof that I'm not.Has anyone else experienced a similar type situation? Is it possible that my frustration with heterosexual relationships is the sole factor influencing this? This isn't something new, and I've actually had weird sexual preferences going back to since I was a little kid.