Hi hon... What a tough situation to be in! I read your hub about this man, and although I don't know who you're specifically asking the question to, I'll offer my thoughts and you can take them or leave them.
I suspect you have a pretty good idea of this man's character already. You worry that he's seeing another woman, that there are reasons he wasn't involved in his own daughter's upbringing, and that he's more of a good-time boy than a good man.
You also have a good idea of what another pregnancy means to your household if you decide to keep your baby. You mentioned adopting the baby out, which could bring a lot of criticism and regret from your other family members and you in years to come, but might also be a good choice. It really boils down to your personal beliefs, and what's best for your children, including the not-yet-born one.
If it was me in your shoes, I'd still date him, but I would NOT reveal the pregnancy until I could get one solid piece of identification that would let me file for child support if he decided to disappear after hearing the news. I'd be looking for a driver's license number or a social security number for sure, in addition to his address. One way to do this is when you see his wallet, ask him if you can look through his photos. If he says he has none, ask if you can snoop anyway to see what he's "really" like in a joking manner. I'd memorize the DL number on the spot and give him his wallet back. If this didn't work, I'd dig it out of his pants while he was asleep. If he awakened, I'd fess up to the pregnancy and no matter what he said, I'd hire a detective to dig up that info.
Just as you have to pay the price for making a bad decision, he does too. And you never know, he might step up to the plate and decide to be with you or to make up for the time he missed with his own daughter, but I'd hedge my bets on behalf of the child that needs protection.
Good luck with everything.