OK, you are gay if you find men sexually attractive and you get off from looking at their bodies. Having a woman stick a dildo up your ass does not make you gay.
The only way to get to one of man's most neglected sex organs - the prostate - is through the anus. If you are like most of us, if you cum at the same time, you will get the most intense orgasm from this.
Gay men will often tell you that they have had sex with straight men. The idea that a guy can have sex with another guy and be straight probably seems ridiculous to most people. But I (i'm a guy btw) have had sex with guys I am pretty sure were straight.
The way to tell is whether they indicate much interest in your body. Usually straight guys are uninterested in exploring your body and are far more interested in you exploring theirs - giving them blow jobs, etc. But what they most want is to be fucked. Experimenting guys can't wait for you to stick your dick up their ass because they want the pleasure of anal sex which women can't give them.
Just to feed your anxieties, hehe, if you discover the pleasures of intense orgasms induced by prostate stimulation, you may become one of those straight guys who starts to pick up men in gay bars, lol! You'll find interest in those nice thick dicks you see in the locker room like you never have before. You may even start drooling along with the gay boys because you know the power it has to plasure you, hehe.
OK OK i'll stop trying to mess your your mind now