Don't know if I am gay

Throwaway account for reasons. I am also going to talk freely and use some vocabulary which you might not find appropriate.So, first some things about myself. I am a 25 year old male, have had several sexual encounters with women over the years, had one sexual encounter with a guy in high school and one sexual encounter with a transexual. I was in an all-boys high school for the first couple of years of high school and had sex with a guy there. I then kind of forget about guys altogether for several years (including not even fantasing about men). Until I found transexual porn. I really liked it and kept watching it. That is why I then had sex with a transexual once.So since my fixation on transexual porn and my sexual encounter with that one dude in high-school, I started thinking I was gay. Thing is: I have never felt anything for a guy in real-life (emotionally or physically). I have never encountered a guy in real-life where I thought: he is hot or I'd like to get to know him or something. Only in porn I like to watch transexuals go at it. I also cannot imagine myself having a relationship with a guy (I cannot imagine kissing a guy or feeling anything more for a guy then just friendship, or I have just not met that one guy). As at one point I assumed I was gay, I tried watching some gay porn but always felt relatively gross after watching it (no offence to anyone or myself ;)) .Over the last months, I have been dating a girl which, for the first time in my life, I really love. We did not have sex yet but I really feel like she is my first real love. The thing I am wondering now is that although I really like this girl, I do not want to start a very serious relationship with her, if I am just going to hurt her sometime when I maybe realise I am gay later.So although I know the only person to know if I am gay is me, I am still asking if some of you guys can relate to this situation? Also: sorry for the very "graphical" vocabulary.