Help him with... what?

He has lived a life just as everybody else has, with ups and downs. Nothing that he has gone through, in terms of life facts, justifies his jealousy, so you should not bend over backwards trying to make excuses for him. that, on the strength of the facts alone. There might be a medical reason for his moodiness (I am not familiar with his illness), but the facts of his life do nothing to justify his jealousy. By using the term "abandonment issues" instead of "jealousy", you made him into a victim and yourself a caretaker - do not do that!