Do the lies ever stop...with treatment?

I am in a very similar situation to much of what I have read on here. My husband and I are actually divorced now. He said he didn't want to, but has been terrible to me. We had an amazing courtship. But marriage was a different story. He ignored me during my whole pregnancy and we lived in hell as we fought false accusations of abuse from his ex girlfriend whom he shares two daughters with. She was jealous and made up horrible lies that hurt the girls, and our entire family. We spent over $80k defending him in court and paying for her legal fees. We won shared custody but lost everything in the process. I moved back with my parents shortly after our baby was born because he needed time and space to "figure things out". I later figured out that everything he says is a lie. He was emotionally involved with a woman during the last three months of my pregnancy and told her how horrible his marriage was and then days after settling in court and giving his ex twice as much money as she was entitled to he started sleeping with her again! The same woman who had his daughters subjected to rape tests and tried not only once to implicate him as an abuser...but three more times over the course of the last year!

He begged for me to come back, still lying about everything. I have no doubt that he loves me, but his impulsive behavior and deceit are unbearable. He has moments of clarity when he realizes how terrible his actions have been, but cannot explain why he does the things he does.

He has admitted that it sounds like he has ADHD and is willing to try treatment and medication.
He actually took the initiative to contact the Hallowell Center and has an appointment in a few weeks.

Is there anyone out there who can speak to the possibility of someone who lies about EVERYTHING being able to change that behavior with treatment?
I'm so tired of worrying that I will catch him in another lie...flirting with his (monster of an) ex, or God forbid sleeping with her again...or the next cute client that walks through his door.

How can I ever trust him again?

Is real change possible?