Final straw?

This is my first post but I'm finally ready to talk, now that my marriage may be over. Together 18 years, married 16, two amazing children. Husband diagnosed 2 years ago with ADHD and taking Adderall and an ssri, although he was diagnosed when he was young but his mother was afraid the meds would stunt his growth so it was swept under the rug. Ironically she is obviously suffering from ADHD as well but would never accept that and I would never suggest it although I love her dearly. I am not allowed to tell a soul about my husband's condition and I often feel so alone and trapped. 

I read books about ADHD but he will not, nor does he want to learn about it. He just wants to take a pill. Despite my efforts, he mostly eats junk when he does eat at all, has a massive sweet tooth, has been addicted to Copenhagen since he was 15, rarely exercises although over the years he's been hyper focused on it. Learning about ADHD has made our relationship make sense to me at last, but I also get so angry that this is the way it will be... Had I known I would have never married him but our children do make it all worth it. In fact the only reason I am sad about my marriage ending is for them. My parents were divorced and I never wanted that for my children.

Over the years I have wondered how we got here. And I've wondered where I've gone. I've lost myself, walking on eggshells and trying to keep him happy. When he is, all is right in the world. We've been through therapy several times. He had a sexting affair, I chose to believe that it wasn't more than that, and his hyper focus on our relationship reminded me of how I fell in love with him in the first place. We viewed it as the worst and best thing to happen to us as our marriage has been much better. I never thought it would happen again. But yesterday I saw a text pop up that I asked him about and he denied knowing this person. He even called the number over speaker and acted like he didn't know her. When I looked up her number I find that she is an escort. And going through phone records today I discovered that their first contact was last summer. No other records but if other texts were via iMessage I will never know. I even tried calling her today but she did not answer. 

He does not know that I know yet. I love him but I hate him for throwing our marriage and family away. I have always warned him that if he ever cheated I would be gone. He even said yesterday that he knows that and he never would. 

He lies about things that don't even matter, so of course he would lie to cover the biggest mistake of all. We have a 4 hour drive home ahead of us today. I can't decide if I will hold my cards close or tell him as we drive.