You're so attached because you see him as your last, best hope.
Note: I am not a doctor. I don't even play one on TV.
But seriously, you may be seeing him as your last and best shot at happiness, and may see anything/anyone after him to be someone who could never possibly measure up.
So! Talk to the guy. And tell him you want to go public because this is eating you up inside. And quit with the bullshit about waiting for his divorce to be final. He is separated from his wife, presumably (hopefully) in the midst of getting a divorce. His wife has got to know you (or at least someone like you) exist. And his kid most likely does, too.
If you are keeping things on the down low in order to spare their feelings, don't. They will be fine, and it will be far worse if his wife or child thinks there's some chance at reconciling when it turns out - surprise! - that's already dead in the water.
And if you are keeping mum because he'll somehow get a better divorce settlement or custody or whatever, talk to a lawyer and find out if it'll make any difference. In a lot of the US, no-fault divorces are the rule, not the exception, so it shouldn't matter. And, I might add, divorce is a far faster process than it has ever been. If this is dragging on for months and months, then something's amiss.