Hello JusJRo, I can partially relate to what you have told us, and now, understand the difficult position you're facing, as I was in a very similar situation, however, I did visit a psychologist for a long time, something your husband hasn't continued to do but what you yourself believe in.
You can care for him as you've said, unfortunately, he needs to step up and get the help he needs, because it won't happen by itself, and although this may appear to happen, there will be many certain aspects that he won't be able to address himself and are pushed aside, but triggers may bring them back, that's why he needs to see a doctor/psychologist.
When he makes comments that he doesn't want to carry on, then you can ring the police, that's what my wife (now ex) used to do and then those statements were not made anymore.
Things can only get better for him when he wants to confront this situation for himself, you won't be able to keep holding him up, whereas if he was getting the help and improving, then you can assist him, because you have your own life to live and not responsible for his actions.
Please stay strong and do what you desire, the only connection is the chain connecting you with him because of your son.