Speak to your friend about whether she would be ok with you getting together, if that happens.
Then speak to him and ask him out. If your friend is ok with it. If she isn't, could he be 'the one' and decide whether it's worth risking your friendship.
If you don't ask, you don't get. She/he can only say no. You'll never know if you don't ask.
Personally, I think life is too short and we need to grab our chances when they present themselves. So, if he makes you feel how you've said, I'd say go for it.