I agree with Callista, this has little to do with Aspergers. Mr. Rath is home with our two and he loves it. He's overwhelmed sometimes, but now they are his obsession, he spreadsheets their schedule and he immerses himself in their activities and he prepares elaborate dinners. He needs his downtime, and his computer time but I do not believe this has to do with just aspergers. Lots of typical guys might feel this way (and women too).
What I can share with you is: The 2nd child is not easier in my experience. The work gets exponentially harder, the price exacted from the relationship is huge. Going from 1 to 2 was harder for me than going from NONE to 1, and that's the biggest transition of your life.
This is not something you go into without a 100% committed, enthusiastic, partner. It's really unfair to your existing child and any potential further children.
I think your only avenue here is to explore with him why he doesn't want children. And the bonding thing concerns me also.