You are exhusted becuase... you are exhusted.
Brains use a tremendous amount of energy as it is. You probably spend your life trying to resolve the irresolvable, trying to think how he can be turned into who he ought to be. Or be compensated for.
And then there is the worried watchfulness. Even if you are no longer aware of it you are probably observing him, his mood and trying to come up with stratagies to avoid him triggering, plus running through disfusing stratagies for all the different ways he'll behave if he does trigger,
That. Is. Knackering.
Would your family come and get you ?
Is there anybody who would drive you up there in your car and maybe come back by trian ?
Can you drive as far as the train/coach station, leave the car for later, get as near as you can by public transport and then have your family pick you up ?
It's not your fault you feel so out of energy love. It has been sucked out of you by an emotional vampire.
It's ok to lean on others who love you as you should be loved to help you put of the mire.
You know how we have those life saving rings ? How we don't expect exhusted half drowned people to swim all the way to the lifeguard's boat, rather we expect them to need help getting to where safety lies so we tend to use devices, or jump in and get them ?
Well this is like that.
First bite of elephant. Tell your family. Tell them you need help to get out. Let them throw you the life saving ring and help pull you and your child out of the cold stormy waters. They love you both. Let them help you.
((((((massive hug)))))))