Hey M.!
I was in the exact same boat you are! :)
I knew that I wanted to have 2 kids & so did my husband, but he had more reservations once our son was born. Our son is fabulous - really well behaved, verbal from an extremely early age, very bright. DH is worried that #2 won't be like Chase (of course they won't!), but he seems to dwell on the negatives - maybe it's a guy thing.
I am an only child & actually was offended one of the earlier comments. My husband has a brother (they aren't all that close), but their family dynamic was quite different from mine which probably contributed to their emotional distance. I appreciate being an only child - it was a difficult decision for my parents to make, but they knew they could only afford one (they were both schoolteachers at the time). Now that I'm older, it might be nice to have a sibling, but it doesn't affect my life whatsoever - I never wanted for playmates or attention. I am far from spoiled (most people are surprised I'm an only). I guess I just wanted to say being an only isn't the worst thing in the world... maybe harder for parents than for the child.
Anyway - I'm now 13 weeks pregnant with #2 & we're all thrilled. Our son will be 4 in 2 weeks, and the spacing is ideal for us. Chase is interested in the baby, he has nicknamed #2 "Sunny" until we find out gender, and he is old enough to better understand that we're adding someone to the family - not replacing him. I honestly couldn't imagine being pregnant with a toddler to chase around at the same time!
My husband wasn't overly thrilled at first - I love the timing, he would have preferred to wait until after the first of the year. He had the same fears your husband seems to have. My advice is just to talk to your husband - I had a lot of luck when I just laid all of my feelings out on the table... at least it opened up the conversation. On the bright side, DH is really excited now - he was nervous until he saw the first ultrasound. Maybe you can find a middle ground where you have a second child, but the timeline is a little lengthier so he feels more confident as a dad & gets to spend more time with your son as an "only." :)
Good luck!
J.
Mom to Chase (almost 4) & "Sunny" (due 6.2.08)