Oh little I understand how you feel.
We have a 3 year old and a 13 month old, and what someone above said about dealing with shit all day etc is pretty much how we feel a lot of the time.
It's bloody bloody hard work at the moment. The housework seems to have doubled, and the laundry tripled.
But, but...we had a conversation about this a few months ago when we got a night out (woop!) and had had a couple of drinks.
Our relationship is nowhere near dead (although our sex life is) but we are both content to let it ride for a while as, frankly, there's so much else to do and the daily grind sweeps everything else aside.
I do think your partner needs to take the long view and realise that there is no need to believe things won't get better again. But when the need for peace and sleep override sex and nights out together etc, I guess it might be hard to see that for some people.
Please have a big hug, we are all just a week of sleepless nights away from feeling like he seems to.
Really, long view. You must get him to understand that; show him this thread if you can bear it?