I think everyone feels at least a little guilt for leaving, but the guilt is better than staying and making yourself sick. I finally figured out that my low cortisol levels, depression, and IBD were all related to extreme stress from living with a husband that belittles, negates and critizes everything I do or say. Get out now and save yourself and give yourself a little peace.
Think of it like this Ashley. The best way that you would be able to help him with his medical issues, is by helping yourself first. Like they always say on airplanes, put the oxygen mask on yourself first. Right now, the oxygen mask that you need is to be away from the level of toxicity you are living in (I know this from experience). And yes he will beg you to change your mind - because that's what is in his best interest. But it's not what is in your best interest ... he will be loudly advocating for himself, so why should you do any different? Once you are healing yourself - because believe me you need just as much healing as he does - you will be in a stronger spot to actually help him medically *if you so desire*. This would NOT mean getting back together with him, but could mean things like driving him to or from an appointment (if it was something that required him not driving after); delivering some prepared meals; running a couple of errands such as picking up medication. Don't read this to mean that you have to do any of this much less all of it - healthy boundaries for you would mean that you choose ahead of time what you will and will not do, and you give yourself permission to say no whenever you are asked to do something that you don't have time for, or just don't want to do. Save yourself. Then worry about saving anyone else.