How to deal with lying and defensiveness?

I am really at the end of my rope and would appreciate any feedback or advice from those who know where I'm coming from.

My husband of 20 years has ADHD. About a year ago, he left me. He was tired of my anger and frustration over his ADHD behaviors. Sadly, I had just found Melissa's book and had a newfound hope for our struggling marriage, but he maintained that the problems in our relationship were my fault (control issues, anger issues, etc). He did start taking Adderall, but otherwise refused to see his part in our problems and walked away from 17 years of marriage. A big reason for him leaving was that he had found a cute young girlfriend. She dumped him after a few weeks, and he then started dating other women casually. After 6 months of this, he decided he still loved me, didn't like being single, and wanted to come back home. I took him back, and am now questioning that decision.

I love him. He's a good guy: fun, energetic, adventurous, and bold. He wants to be (and often is) a good dad to our kids. He is very impulsive and prone to lying. I don't know how aware of this he is. He is a highly compartmentalized person. He hides things away, and once I discover these secret things (or even get close to discovering them), he becomes angry, defensive, and verbally abusive. He throws things. He tells me that I am horrible. He threatens to leave me. 

Recently, he asked me to sort through, open, and organize about 2 months of his unopened mail. In that stack of mail I found a poem that he had written for his ex-girlfriend (the one he left me for). It bummed me out to see it, but I got over it (the relationship is physically over, though he's still hung up on her) and continued to clean up his mess. A couple weeks later, he gave me an edited version of the same poem. I tried to be happy about it, but was pretty hurt and told him about the poem that I had found. He became furious, called me ungrateful and mean, angrily denied that such a poem had ever existed, and accused me of having mental problems and making things up to hurt him. This event has played out many times in recent years (when I discovered he had slept with an old family friend, when I discovered that he had gone to a "massage" parlor in Vegas, etc). He denies any responsibly, lies, and accuses me of having trust/psychological issues.

He denies that he lies. He denies that he is defensive or angry. He won't read Melissa's book with me and won't even discuss ADHD issues if they negatively affect me (but will discuss what a gift it can be), and he actively avoids me when I'm upset by something he's done. Does this ring a bell with anyone? Is there hope? When I ask him to confront his distance from the truth and deal with his anger, it backfires in a powerful way (ie, that I'm crazy and he'll leave me if I don't stop being crazy). I don't want to live like this. Any suggestions? I don't want to give up on him.

Thanks for listening. I know there's a lot of pain and frustration out there. I want to improve our marriage, but I feel very alone in this effort.