My sympathies! And yes, it is a challenge when they are toddlers. Are you a SAHP, or do you work, may I ask? Obviously it's a bit easier if a SAHP - I've done it both ways.
Those weeks he is at home - enjoy them. And make sure you are both on the same page that when he's home - he's on deck and doing all he can to lighten your load with the wee one, and with the house.
Um, don't obsess about keeping the house in show home state. Some days it might be all you manage to get you both fed and dressed. That's okay. Hell, you might skip the dressed bit. That's okay too.
In the weeks he is there, if you can, cook some meals that you can freeze half, so you can just pull a portion out the freezer for a main. (Spag Bol, lasagnes, and curries are really good for that). A cooked chook from the supermarket and salad and new potatoes are your friend. Oh, and ready meals and pre-prepped veges!
I tended to meal plan (it usually went south by Thursday, but hey, it's the thought that counts). Routine is definitely your friend, as are to do lists.
Make sure you treat yourself to little luxuries if you can afford them, and well done presents. They don't have to be huge.
I also did meals that the kids loved that we only ever had when Daddy was away - much to his chagrin! Things like marinaded chicken with corn on cob, and mashed potato and gravy. (This house is far too food focussed). Have some good movies or netflix shows that you wouldn't normally watch if he were there to look forward to. See if you can line up friends to come round for a session.
Oh, and I built in rewards/treats for the kids too - there were shows we'd binge watch together, like (ugh) Dance Moms. And then when Daddy got home we'd make HIM watch them (insert evil cackle here).
Try and make sure that most days you get out the house, even if it's just to the supermarket or the park.
Any offers of help or childcare, grab 'em with both hands, before they have a chance to regret it. . .