Unfortunately Jen, he is a grown man as you know, and if he does not wish to change he won't, and there's nothing you can do about it. He perhaps needs to reach some sort of "bottom" as far as the IBS or diabetes goes, becoming extremely ill before he makes serious changes. All you may do is be there for him, and try to be happy for yourself. Make certain you are happy and do things you enjoy daily, apart from his ups and downs.