gangle, sweetheart, next time your dh is lying in his pit 'resting' until gone 8, dump both children on the bed and leave the house for an hour. go and grab yourself a coffee and a bagel somewhere.
he needs a wake-up call, and he needs one fast.
does he work weekends? if not, find a friend and take the little one with you (if bf) and leave the toddler with him to bond for a day or two.
no-one will die, and he might even discover he's actually a parent instead of a single bachelor who happens to live with a mother and two children.
no, you're not alone. being a mum to two tinies without support is the hardest thing in the world - mental illness highest in this demographic for good reason.
but get a grip of your husband, lady. it's easier to do as a team.
another tip is to leave him with the dc's for half an hour when he walks in the door of an evening. take yourself for twenty minutes fresh air without being responsible for two other lives. jog? walk? go to the shop for a jug of milk, whatever.
and just be nice to yourself - if you need to all snuggle up in a duvet with the tv on in the afternoon, do it. (dd1 didn't sleep during the day at all and she drove me nuts)
but please, please, sort that man out.
you can see the doc about antidepressants etc, but tbh life would be much more bearable if you thought you had someone watching your back.