Feeling confused and deflated, advice needed

Finding myself so confused and deflated, and completely unsure what to do. I've posted on here a couple of times only but have taken a lot of heart from the many posts I've read over the last year or so. I've been married for 20 years to a man who was diagnosed adhd a year ago at the age of 48. Together we've faced a lot of big challenges, particularly in the last 8 to 10 years. DH is an alcoholic who has been sober nearly 4 years after some really close calls. He's been involved with numerous women over the past 8 years as well, acting out with both emotionally and physically relationships. The most recent one is ongoing - coming on to 5 years now, off and on. Two and a half years ago my father passed away after an intense year and a half long battle with cancer. I was responsible for a lot of the support and big decisions for my parents during that time. I confronted DH about the most recent affair the same weekend that I had to put my dad into palliative care. The illness was excruciating for my dad and also excruciating for those of us who had to watch it. I couldn't handle the pain of my father's illness and the pain of my DH's infidelity at the same time so I packed DH's bags and made him leave. It was a lonely and painful time - I am so not even close to healed from that winter.

Two years ago, sixth months after my dad's death, DH came home at his request. I, foolishly, picked him up from the girlfriend's apartment - he had been boarding in a house for the 7 months of our separation, not staying with her, but the term of his lease was up and so he went to her house for the day because he "had nowhere else to go." Now, 2 years later, their relationship is as strong as ever while ours is falling to pieces. There have been so many aha moments and ups and downs in the meantime: he's been in and out of counseling with 2 different therapists, he joined, and then left, a support group for sex addiction, I've been mostly regularly seeing a therapist, we've had couples therapy but only occasionally, he realized last spring that he has adhd and sought a diagnosis (which was temporarily liberating and uplifting), he was on meds for a few months then decided to quit without talking to me, etc. and on and on. He's pulled away from the girl and then pulled away from me instead, and back and forth. At times I've felt that I'm in a marriage with a man who is working so incredibly hard to get his feet under him, who is honest with me and respectful of me and of himself, that I can begin to trust and be open, and so on. At other times I think what on earth am I doing? This is one of the latter times.

He becomes angry with me constantly, turning away and refusing to talk with me, leaving the house for hours, sleeping in the guest room for days or weeks at a time. Since he went off meds in February he's spent more days avoiding me than being with me. One of his "best" coping strategies is to project and that's one of the things that's happening right now. The thing is, he's so incredibly brilliant that he projects onto me his problems, but only when there's at least a grain of truth or accuracy about them. For example, he's been taking his intimacy away from our marriage and sharing it with someone else but his response whenever I express that I am upset is to say that I never share myself and true feelings with him. Well, sure I don't! First of all, you've betrayed my trust over and over and over again (of course if I actually say that out loud, he's out the door) and second, my own protective coping strategy in life is to shut down, and the thing is that I've had lots of cause to protect myself! 

He's so filled with shame and self-righteous anger, and the two take turns in presenting themselves. He can immerse himself in either of those feelings and then the only thing that makes him feel better is contact with that woman. He realized last year that, when he thinks of her, he feels just as high as if he was on his 2nd or 3rd pint of beer - the dopamine reaction. For a while then he stayed away from her but now he's forgotten that he had realized that. Good grief.

I get and agree with all of Melissa's advice, I take great pains not to react and it's all good with respect to the little stuff. But wow this is so not the little stuff and I feel like the world's greatest most incredible fool. My DH just informed me, a couple of hours ago, that he's going to go this summer, during our holiday, drive 11 hours and spend the night camping near the spot she'll be working, and then drive her here to our city the next day. I calmly said that, since she's just "a friend" (the relationship stopped being physical 3 and a half years ago because she decided to stop that aspect of it) then I should be a part of a summer jaunt to this lovely spot. He said I wasn't welcome. Really. My response was indeed calm - I said that wasn't okay and indeed not normal, that we are married and so for him to take a trip during our vacation with another woman was not what married people do. He interrupted to say, once again, that I don't share myself with him. I said not to do that to me, meaning that he shouldn't interrupt me to throw an accusation at me, and he left the room. I followed and simply continued what I had been saying only to have him tell me that he had stopped listening several minutes ago. I freaked. I'm so so so tired of being treated like that. 

He accused me of only ever being "okay" and smiley, which to him is a bad thing because he can't see how anyone can live in the moment and simply be happy and so therefore I must be "faking" it which makes me insincere and phony, and dramatically overreactive in his opinion. I am absolutely a dramatically reactive person, but, given the circumstances, am I overreacting? I don't think so. But then I seem to have no choice but to either disengage and be blamed for removing intimacy from our marriage, or else freak out and be blamed for that too. Here's the real kicker: he doesn't seem to remember the many times I've shared with him, gifted him with trust, forgiven him, accepted him, and opened up to him, even when I remind him of those moments and conversations - I HATE this faulty filing system!!!! I just wind up deep in a pity party, feeling so many ways a fool, and then I've got to get up every morning, put on my game face, and go to work. I come home to an empty house and then an empty bed and then he blames me. Tonight I asked why on earth he had been so insistent that we reconcile two years ago, why is he even here? How I so often wish he would just go, just leave. I have tried to make myself move out but can't put our 16 year old through that again. But I feel such a loser - what am I going to do, just sit here while he goes off gallivanting with his girlfriend this summer? How can I do that? And what has happened to the cozy, loving, fun and adventurous relationship I thought I was signing up for all those years ago?

Now he's said that the reason he's mad this week is because I posted on facebook on father's day that I really missed my dad and that I feel fortunate to have been his daughter. DH said that "broke his heart" not because he empathized with my pain, no, but because I put it on facebook but I allegedly don't share my grief with him. So he stopped talking to me again this week and then planned a trip with his girlfriend. Have I fallen down the rabbit hole? Thanks for reading,

Stuck and confused