He asked sex from me and he's my best friend.

[driftwood]

I feel really weird and I'm thinking about it all the time.
I don’t understand why did he ask it from me? I'm his best friend after all.
Why didn't he go to the places where there are many homosexuals, like gay bars?
Does it mean he thought I'm gay?

No, he doesn't think you're gay, and he isn't gay either. He's bi-curious. It's very common among straight men. Psychologists used to call this "latent" homosexuality. A lot of Men never experiment simply because they would not feel comfortable walking into a gay bar. He asked you because you're his best friend and he trusts you. He asked you, you answered, and that's all there is to it. Forget about it.

[sillyboy86]

As many said, he's probably bi-curious.

Why you and not 'a random one' in a gay bar? Cause he believes in you, you're his best friend, not a random-dirty-guy who only wants sex. Maybe he is also a little attracted by you, cause you're a very good person to him, so he tried. Nothing strange in my opinion.
You refused cause you're 100% straight and he apologized for his mistake. He doesn't think you're gay.

Don't overthink about that, you're his friend and he's your friend.
Now you only have to support him if he's afraid of coming out or something else about his sexuality. Like you do every time, being his best friend.