Have you ever dated a best friend, only to regret it?

I chose not to date my best friend when he was interested in me a while ago because we have the most amazing intellectual connection I've ever experienced, and I'd rather have it forever in a platonic way than to squander it on a short romance. I made the mistake before of dating a best friend, and we aren't even friends anymore (breaking up was even worse than it should have been, because I was losing my best friend and my lover all at the same time). Do you think it's a mistake to date best friends, or is it a good thing?