Can't take the lies

My husband and I have been together 13 years. We've been through it all. Many years ago, he mentioned something about having ADHD. Neither of us thought much of it and that was the end of that. Fast forward to now and we're both seeing it so clear. He has yet to be officially diagnosed, but I am 100% certain he has it. Everything I've read describes him to a 't'. For the past few years or so, I've thought he was a full on narcissist. It wasn't until recently that I realized its his ADHD. However, I don't know how much more I can take. He lies and lies and get the point. I'll ask him something and he'll swear up and down he didn't do it. It isn't until I show him proof that he admits it. He's struggled with porn for our entire relationship/marriage. He claims he hasn't looked at it in over a year, but I don't believe him...thanks to Google's incognito mode. I always find odd things on his phone and he says he has no idea how they got there. I feel like I'm fighting a lost cause. It doesn't add up. I WANT to leave him, but I'm scared beyond measure. I love him, but don't know how much more I can take. I just caught him in a lie about looking at certain friends on my Instagram. Yes, its petty, but it hurts. It wasn't until I told him I knew that he admitted it. Is compulsive lying part of ADHD? How do I deal with it? If he lies over little, ridiculous things, I have a hard time not believing that he's lying over much bigger things. He turns and twists and manipulates everything to where it all ends up as my fault and I'm the one begging for HIS forgiveness. He has zero empathy. He takes and takes, but never gives back. I love him- but I feel like I (and our kids) deserve much better.