I hope you’ve been able to consider your options. It’s not fair on you or your own pet. She sounds like she needs a lot of love, care and training, poor girl. Please be open to discussing rehoming , it’s not the end of the world for the dog, but a fresh start.
In my opinion, as someone who has two rescue dogs, and further family members with another six in total, loving people are waiting to adopt dogs. These people are vetted to show that they are suitable. Dont be afraid to simply phone to talk to the best rehoming centres. They will understand your predicament, and not let your husbands dog leave until groomed and assessed. It’s not in their interest to place a dog in the wrong home to have it returned. Often dogs are fostered to improve socialisation and training.
There are admin people on this forum who are involved in rehoming cockers, and I hope they chime in. If not , start another post . One of my dogs was previously totally neglected and antisocial , until signed over to the rspca. I adopted him immediately and with time and and training he is now fantastic .
I feel that your dog should come first , with you. Your ex should not dump his difficulties on you and leave you feeling so upset and guilty. His dog needs a better owner than him!!,
No offence meant if I’ve got this wrong.