Mid-Life Crisis From Hell

I need to really vent (scream?!) here, so I hope what I'm saying makes sense.  I guess I really need to know if I'm losing my mind here, or if I have a real problem on my hands.  My husband and I are 55 years old, we've been married 20 years, second marriage for both of us, and up to the 15 year point, it was a wonderful marriage.  He was diagnosed with ADHD about three years ago.  I've lived through his having an affair, his cancer diagnosis, not being able to count on him for anything, his focus on everything else but me, his need to control, and his erratic attention span.  And the only thing that has helped me keep my sanity is reading the books on ADHD.  But now I believe we're living the mid-life crisis from hell, and I'm starting to wonder if my husband has "marital" ADHD, not regular ADHD.  The only place his ADHD really seems to come out is with me.  The reason I know this is because anyone else will tell you what a great, loving and helpful man he is.  I guess I was at the wrong pier when that ship came in.  This mid-life crisis (if that's really what it is) has been going on for about 18 months now.  He's become very selfish and self-centered and openly gawks at women when I'm standing right there.  And then he has the audacity to deny it when I'm watching him do it!  He even did it one time when we were in church!  I don't want to go places with him anymore because I'm furious (not jealous) and embarrassed at his lack of respect for me.  And he now says he doesn't want to go any place with me because he feels me watching him.  I wonder why?!  I even tried role-playing with him, and he doesn't believe he's as bad as what I'm showing him, so he sees no reason to change.  My husband stares long enough to get the woman's attention, and she's probably staring back because she's wondering what this guy is doing!  I'm not saying my husband isn't attractive--because he is.  But why would he be acting like a 19 year old walking hormonal teenager!?  I'm beginning to wonder if he's involved with another woman again.  I've already asked him if he's feeling unappreciated at home, if there's something I'm doing that's making him feel shut-out or need to look for attention elsewhere.  And he responds that he's very happy with me.  He tried to convince me that it's normal for a guy to check out women like that; men are "physical" creatures and if they see something attractive, they instinctually look.  Well, women look too, but it's extremely inappropriate for a married individual to gawk like they're sending the "I like what I see and I'm interested" message.  Anymore I just wish he would just go away; it just hurts so much.  Where is the guy I dated and fell in love with?!  Is it me?