Thanks for responses everyone. I've told him that he'll get out what he puts in - and that he just has to accept that that means engaging properly when he's with her. I linked it to the whole deal where sometimes I get nothing done because she's been really demanding - he knows that that happens, but I don't think he really get what that means in reality. He can't just sit in front of the telly and concentrate on a programme with her sat on his lap 'watching' too, because that results in shouting/squealing and him wishing she'd shut up. He desperately wants our evenings back, and so do I... but it's not going to be forever, he should try to enjoy this time.
I saw him for a few minutes at our building site of a house today, and he brought up the conversation. I suggested that he might have PND, he agreed that it might be possible. I used FATE's comment that if I was saying these things, he'd send me to the doctors. I skewed my comments in the direction of his not letting our other 'life stuff' (building site house, money, living with parents etc) build up into causing depression that prevents him enjoying his time with her.