If your husband is adamantly against homeschooling, have you asked him what solutions he would try? He may have ideas the two of you can discuss, and if he doesn't, you might begin a subtle campaign of making him more a part of the morning drama so he is aware of what your son is going through.
We had a bad fit one year with my youngest, and we had a lot of Yellow Bus Fever that year as well (as in the symptoms passed once the bus passed our house). Some days I insisted he go, and other days I would go sign him out for "appointments" around the time he had the subject that was creating most of the problems at school.
More homework for a 5 year old is not a good accommodation, in my opinion. And if the teacher isn't receptive to dealing with the stress your child is experiencing, I'd enlist the school counselor who will be more motivated to deal with your child's mental and emotional well being and may carry more clout with the teacher.
The advice to stay within the truancy laws is good - but within those contraints, I'd do a lot of zoo, museum, and explore days from now until the end of school. But I'd initiate them before the crying starts so that your very bright and perceptive child does not decide to use crying to manipulate.
The year my son had such a hard time, his grades were horrible. I was fretting over this until my husband pointed out that no college looks at the second grade GPA. It put it in perspective. I quit fighting the teacher and just made sure the damage to my son was minimized. The next year's placement was much better, and the Yellow Bus Fever disappeared with it.
