I agree but if you never go for it with her you're going to regret this for who knows how long.

It would be better for you mentally and emotionally to just go for it with her (while she's still in the early stages of just dating this new guy) - it would be better for you to just go for it with her, even if she rejects you. This way you can MOVE ON knowing that she's just not the one for you, know what I mean?

Whereas on the other hand you're going to be moping around for who knows how long always wondering "What if" and always kicking yourself for not just going for it (much like you were in this post)

So I say: Go for it, you have nothing to lose and everything to gain.