I don't want my marriage to end, but understand

We're married more than 15 years. I was diagnosed ADHD 2 years ago, and accepted the diagnosis and meds. After a rough transition, My life has changed for the better in so many ways. My job went from shaky to great, I gave up alcohol, watch my sugar intake, exercise regularly, and always have done my fair share of house chores. It's not enough for my wife. She wants me to suddenly not be ADHD. She wants me to never again make a dumb comment. I'm supposed to become perfect.

I think our marriage is great, and we have great times together. The last few weeks have been wonderful. Yet tonight one little discussion went off the rails. I stayed calm, and tried to keep it from escalating. She wanted it to be monumental. 

I can't handle the burden of carrying her happiness, of it somehow being my responsibility. A few months ago, I told her in a loving way that she was free to leave me. I wouldn't hold it against her. She declined my offer. But it's just not working, and I wish I knew I was ADHD before I was married so I'd know to stay single. How do I end this? Should I end this? She loves me, but the constant pressure of having to be perfect is killing me. I should have stayed single. Yet I'm afraid to be alone.