I really don't think you have a healthy mindset around romantic relationships. Are you unwilling to pursue a relationship with him simply because you're scared of breaking up and "losing" your friend? Afraid that dating, period, means an end to friendship and that romantic relationships are totally different from friendships? Or are you simply uninterested in ever dating this friend because you could never and would never have romantic feelings for him. There's a difference between all three things.

Believing that romantic relations and friendships should never mix is probably going to lead you to a life of never having any satisfying romantic relationships. I'm getting married next year, my fiancé is my best friend. He was my best friend before we started dating- we were even roommates. We've now been romantically involved even longer than we were ever friends, and I have no idea where I'd be if I'd never confessed to being attracted to him. I know we'd probably not still be close friends the way we are, because we've now moved cross country together TWICE. That would not have happened if we'd simply "stayed friends"

These friends you mention in the past that you had feelings for but crushed those feelings, are you still friends with them? Any that you aren't friends with anymore, is that fundamentally any different than having dating and then broke up? Have you considered the possibility that if you'd asked them out and started dating, you may have ended up being close & being friends with them longer than you did without dating? You could have ended up marrying one of them, and would still be enjoying that relationship (and friendship too!) to this day. But you'll never know because you didn't take that chance. Every decision in life comes with risks, and if you avoid ever making a decision, then you've made the decision to stagnate