I realised that I had to end it when my H revealed just how useless he is at handling children.
We were in London, post a children's theatre show, having lunch in John Lewis on Oxford Street. We have 3 dc, all 3 have ASD.
Towards the end of our main course, ds (then 2), needed a nappy change. H took him, leaving me at the table with dd1 (severe ASD) and dd2. Fine.
20 minutes later, I get a phone all from H. I am still at the table, fielding ever more hysterical questions from dd1 as to where H and ds are.
H is frantic on the phone. Ds had had a really messy nappy, which had leaked all over his clothes. H snapped at me to sort it out, then got really shirty when I refused to pack up the table, pay the bill (without dessert - unheard of in dd1's experience, so would have cause a huge scene), go and buy ds new clothes, and deliver them to the baby change room. Apparently, this would be far easier than H, umm, getting ds cleaned up, putting a fresh nappy on him, and walking him out of the baby change straight into the childrenswear department, buying new clothes and dressing him. Because what parent is going to think anything at all of a (clean) toddler being led through the babywear in search of new clothes. Most would be thinking 'there but for the grace of God...' or 'ha ha, I remember when I had to do that'.
He was snappy with me for days over that one, as he truly believed I was unreasonable to refuse to pander to his ineptness.
And that was when I realised he would never actually fully do his share. Everything with the dc would always be my responsibility, or my problem to solve. He wasn't helping at all, and was in fact just another person to be responsible for, and I don't have the headspace.