How do you ended up being gay (or bi)?

Here's a random question that has been circling on my mind lately: How do you guys ended up being gay (or bi)?From my personal experience, I have been straight for 21 years until the start of my college studies in the first semester where one of my roommate began to ask me whether if I masturbate or not. I was just lying by saying no, thinking that would be the end of it. However, I only found out from that same roommate that he had been using my hand to masturbate himself. Since then, he's been asking me to do fellatio on him. The rest is history...