Well, IF (heaven forbid) I got pregnant again, both my husband and I would be upset. He had the V done, but so did his dad (had one more about 2 YEARS later) and so did his brother (had one more about 2 YEARS later). Don't mean to scare you, but that does not always work. In our case, thankfully it has worked... so far. (fingers crossed)
But in your situation, it is what it is. It's really hard to accept that your life is going to change in a way you never thought (or initially WANTED) it to. I know that's how my sister-in-law felt when she found out she was preg for the 3rd time. She was very upset. But ya know what? Their 3rd fits into that family (obviously). It was meant to be. =]
I'm sure he will be okay in a while. Give him time. It sounds like this is quite the shock. If you have a strong enough marriage and strong enough relationship, you WILL get through this. Be patient with him.
Best of luck to you!!!
(BTW... are you?)
~K. =)