Oh dear - I do feel for you, as I've been in exactly the same situation. I hope we're coming out of it, and I do feel quite differently to some of the other posters: I'll try to explain why.
My dh and I have been together for 13 years, and I've been off contraception for 4 years (I've just turned 43). I had a mc nearly two years ago and, earlier this year, when my cycle still hadn't settled down, I had various tests and was told I was peri-menopausal, and we should think about adopting.
Long story short, I fell pregnant (like you, I didn't know my dates) and my dh fell apart. He said the only reason we'd kept 'trying' was because he couldn't take how upset I was over the mc, but that he'd never wanted children. On one hand, I wanted to throw things at his head, yell about what a stupid ba*rd he'd been and why hadn't he told me, rather than letting me carrying on hoping. BUT - on the other hand, how could I really let rip, when his reason for carrying on was in trying to make me feel better, regardless of his own feelings. (Don't get me wrong: I've had several episodes of leaving the house in hysterics, and not knowing how I was going to face him.)
I've had weeks of sleepless nights, wondering how I could afford to rent by myself, should I terminate, whether he'd be happier without me (we have a fab relationship otherwise), would I be able to work full-time with a baby, how soon should I go back to work..... you get the idea.
Anyway, he has now admitted he hasn't been able to cope, and has been diagnosed with moderate/severe depression - he's had a lot of things building up, and this tipped him over the edge. I do think he feels better, even just starting to admit that he couldn't cope - and I think it's a very male thing to not be able to admit weakness. He's scared about how we'll cope financially, that our lives will be ruined and we'll never be able to have fun again. I do think we might be turning the corner, but he still has really rough patches. For me, it's felt really important not to add to the pressure he's been feeling, but to tell him I do still love him but I think he needed to get help. It took a visit to his parents, who got through to him in a way I couldn't. I know it's really hard, but do you think your dh may have gone into panic mode, and needs some time to adjust?
Of course, all our relationships are different, but I did just want to suggest an alternative view. The decision is yours, but please try to give both of you a little bit of breathing space, and do think about talking to your GP yourself, as you'll need lots of support to get through this.