Why is it bad if I leave the marriage?

My husband was recently diagnosed with ADHD a few months ago. We have been married for 21 years and have a 17 yr old and a 5 yr old.  We have been in couples therapy for 3 years going in circles until finally figuring out he has ADHD. I think my therapist new all along but knew that if my husband didn’t come up with it on his own he would never have believed her and wud have ended our couples therapy immediately.  Only because all these years of struggle have been due to the fact that I am crazy, emotional, depressed, and unable to handle life. According to my ADHD husband of course. and after reading all these other blogs I am not alone. He is on Aderol now tryin to get the dose right and wants a new start to our marriage. But I am tired, emotionally and physically. The day he was diagnosed was the day I had mustered up the strength to end the marriage. But now I’m supposed to try to make it work. Why?