I don't know exactly what your situation is, but if he is not someone you owe something to, the optimal solution would be to apply to YC first. If you're accepted, you can invite this would-be investor to Demo Day, where he can compete with all the other investors to fund you; if not, he's plan B.

Note that this assumes that you're not indebted to the guy in any way-- that he is simply a source of money.

BTW, 3 years is a lot of money. It suggests to me that you're either raising too much or (more likely) underestimating your expenses.