Theory & reality are 2 very different things. It's one thing to talk about him being the SAHP & you going back to work, but it seems reality is a lot harder for both of you than you could have imagined. It sound like neither of you are getting much sleep which makes things a heck of a lot harder. And I agree with suggestions that maybe your dh could have PND or depression or he's just struggling. Being a SAHM is hard, but it's a lot more socially acceptable to be a SAHM than a SAHD. There aren't many dads that go to playgroup with their bubs ... I'm yet to find a playgroup for Dad's anywhere near us (my dh was a SAHD 2 days a week for 2 years).
Having you gone for 11+ hours a day is a long time for the 2 of them to be on their own too. 11 hours must seem like forever for him.
I suggest having a calm and non-judgemental discussion about it all is a good idea. Telling him to step up is not going to work. He is trying, really hard, and not managing. Reinforcing that will just make him more upset. Maybe family day care for 1 - 2 (or 3) days a week would be a better option now that the reality of everything has sunk in.