Retro - I sympathise, I had a similar reaction, when I told DH & we did the pg test - he went into a 3 day mad panick of saying 'but I don't want another child, I like it with 2!'. This was after having discussed going for #3 for about 2 years and him always saying that he'd like to have another one and after agreeing that we're now going to 'go for it'... Wasn't very nice cause he made me feel as if I'd 'tricked' him into it somehow.
I now think he just panicked about everything - money, car size, holidays, number of rooms in the house, university fees, number of grandchildren, you name it! Not sure why it happened but I'm glad to say he's calmed down now and seems to have come round again to wanting & looking forward to #3... MEN!!!
Anyway, big sympathies from me, I know it's not great when you're really happy and partner isn't - I hope yours is going to come round to the idea soon...