I really feel for you. This might be a v unpopular opinion, and bear with me (because I intend this to be supportive of you) but.... I also feel for him (to a degree...read on.)
He has been honest with you in that he didn't/ doesn't want this baby, and isn't happy about it- and he's allowed to feel like that. It's OK to want your family to stop at the number of children that you have agreed upon (assuming you had both agreed this- and had you ever discussed what might happen if contraception failed, as condoms sometimes do?)
It's also ok for him to see abortion as the destruction of a bunch of pre-viable cells, rather than as a 'wee innocent baby' (unless this deviates from strongly agreed ethical standards that you have always understood you possessed as couple) and it's ok for him to tell you that he would rather you had an abortion, and that he might not want to be in a family of three.
I also don't think he's being unreasonable in finding it hard to engage in bump-rubbing etc- why should he be fake and touch your belly and try to bond with a baby he has made clear he doesn't want?
However, he is also behaving quite badly in some aspects of this. I am confused as to why he is acting up as the doting father in front of your other kids and encouraging the name-picking etc, if his ultimate intention is to largely ignore this newborn or run away- what message is he trying to send to you and them? It's as if he's already decided he'll go along with things after the birth, but he's sure as hell going to punish you and sicken you with worry in the meantime and ruin whatever enjoyment you might have had during the pregnancy. That's not fair.
So, what can you do?
I think you maybe need to say to him that you appreciate he's in a hard situation and you do take on board his feelings, but that you're not going to keep hassling him to support you- you can take a horse to water, but you can't make it drink.
Next, I think you need to do as much as you can to ensure you are supported but without recourse to him. Do you have friends family who can help with the birth etc?
There is, of course, every chance he will fall in love with the baby when the time comes, and the way he is acting around your other two suggests that he is setting himself up to be Father of the Year 2016 when it all comes good. However, you have to start preparing yourself for the possibility his behaviour doesn't change after the baby is born, or that he leaves or becomes impossible to live with. I guess you also have to ask yourself whether you want to be with a man who would punish you like he is currently trying to do- because the time is coming when he needs to shit or get off the pan. Commit to whether he is in or out, and before you are in throes of labour and having to deal with a newborn. I think you need o have a tough chat with him and then decide whether you are wiling to let things run while hoping for the best after the birth.