I saw my best friend's dick and ever since I've wanted it

My friend and I are both over 19 years. You should know that I'm heterosexual.

Three weeks ago, I had a party with some friends and we drank quite a bit. My best friend ended up really drunk and when he went to the bathroom he couldn't aim. Of course, everyone could see how drunk he was, but no one did anything, so I had to. I tried all sorts of things, like making him sit down to pee, but he kept peeing, so we changed our plan.

He stood up, holding onto the wall, and I had to hold his dick. At first, it disgusted me, but the more it went on, the more I liked it. Just to be clear, I didn't do anything else besides hold it. While holding his dick, I realized it was really big and especially thick. I don't know how, but it turned me on and I got an erection.

Since that day, I have the image and sensation of his penis in my hand, and I can't stop getting hard just thinking about it. I think I'm becoming bisexual.