I don't really have any advice but I know I wouldn't be able to look him in the eye having read the messages and not mention it. I would be so so hurt and would not be able to move past it without bringing it up. Whether thats the *best* thing to do, I don't know, but to me it'd be like knowing he'd cheated on me and not talking to him about it.
And as for him being tired and needing sleep, yes I'm sure he was very tired but the reality is, we ALL get tired, especially working and taking care of a baby (at the same time!) that doesn't sleep much, I'm sick and tired of men saying they are tired like we don't get tired too! Anyway, obviously I have my own issues in that department, but what I'm saying is don't feel bad for expecting more of a contribution from him, it should be a partnership, not everything your job and him being a 'helper' when it suits him.
Hope you can sort this out and agree with PP to go with your gut.