The actual most attractive thing in the world is sincerity. If you feel like you come off as creepy to people, it’s probably because you’re psyching yourself out and feel like you have to perform when you talk to people about your feelings. Just keep it frank, keep it short, say the thing you mean in the best, fewest words possible.
In this case, maybe, “I’ve been having a lot of fun hanging out with you and I like you, man.”
OR, if you’re nervous, let him know! Open with, “This makes me nervous, but…”
This dude’s your friend, he’ll get it.
And if he doesn’t, on to the next.