titan, having sex with a strap-on does not mean you are gay. It just depends on the relationship you have with your partner. I am 100% straight and have received anal sex from my wife. It is amazing! We have been married for a very long time and both enjoy trying new and kinky sex acts. Our sex life is anything but boring. Any type of sex with a loving partner is always great.
You're forgetting that sex is more mental to females. Just the thought of dominating a guy can make a girl orgasm during strap-on sex. Also the base of the strap-on tends to be situated on the girl's pelvic bone which sends waves of stimulation to her clitoral nerves with every thrust.
I think in order for it to be "gay" you'd have to be with another guy. If it's your wife/gf, then it's just being curious or adventurous. If it's just for cash, then yeah, you're being a ho, but that's cool, too. I enjoy anal stimulation a lot, but I don't have thoughts about men while receiving it, so I'm guessing that allows me to remain straight.