Looking for some support and answers....please.

Let me apologize in advance if this is long, I'm really in need of some help.  My wife and I have been married for just over 16 years and have two kids:  14 year old son and 12 year old daughter.  We separated in October of 2010 and we knew there was no way our marriage was going to work, so we decided to call it quits.  My wife has been diagnosed with ADHD and has previously taken medication for it as well as received counseling.  The combination of the two helped tremendously and she was a completely different person.  She was thoughtful and attentive and talked and listened and enjoyed sitting down and really spending time with us.  However, it's probably been nearly 8-10 years since she's taken the meds or had counseling.  We did a lot of research together on ADHD and the impacts it has on life, marriage, children, etc.....but nothing worked.  My wife turned into a self-professed "adrenaline junkie" and basically disappeared from my life even though we lived in the same house and remained married.  She is on-call 24/7 for 3 jobs one of which include a volunteer fire department.  My wife has told me repeatedly that this is the happiest she has ever been in her life and will not change.  I felt (and still feel) extremely alone, isolated, unloved and not important to her.  I have so many stories of forgotten committments, important life plans we agreed on that were abandoned, missed suppers, birthdays, holidays, coming home late and the like.  I have tried everything I can to try and talk to her but she simply sees me as nagging and controlling and most of our discussions she tunes me out and honestly never really remembers what we talk about or agree upon.  She repeats the same scenarios as listed above and it just spirals from there.  I'm not totally blaming her, I know my reactions play a part in what happened between us, but what I cannot comprehend is if she knows her ADHD makes her spin out of control (again, her words - not mine) then why would she not want to seek/continue help again?  I asked her those specific questions myself and she had two responses:  1.  She heard/read/discovered that the ADHD medications sometimes have a side effect of weight gain - which she is mortified by.  She used to be quite big at 300lbs, but is now down to probably around 160lbs.  She says that her completely active always on the go lifestyle has done that for her.  The second reason she gave for not wanting to treat her ADHD is that she doesn't want to change the way her mind works and she's happier now that she's ever been.  Is this normal?  Is it healthy?

Here's where I need the help. She has "fallen" for another man that has been friends with us for a couple years and cannot stand to be apart from him.  We had come up with a decent plan to get our things in order (fixing up the remaining repairs on the house we lived in together before I moved out, selling it, separating our finances, etc...and filing for divorce ourselves and not turn this into a battle).  And this plan was working very well up until the last week or so - about the point where she started spending a lot of time with the other man.  In our plans upon separation, we both strongly agreed to do this the "right way" and not involve other people in our lives to complicate the divorce process - and by involve I mean date/sleep with/that sort of thing.  We both talked about the fact that how we end our marriage is nobody else's business and we didn't want to take the chance of having someone else involved who would give their opinion on why we were doing things the way were and/or give advice on how we need to do things.  Then suddenly, out of the blue last weekend she comes to me and tells me that she thinks she's about ready to start dating but doesn't really have anyone in mind.  Once again, being totally confused and hurt by the fact that once again she wants to completely ignore the impact this could have on things, I am not happy.  We talk/argue/fight/cry/discuss and she says she won't be dating anyone until we get our lives separated such as bank accounts, cars, houses, etc and that she's not going to put herself in a situation where she could lead anyone on or get involved with anyone.  Then, two days later I found out she had been spending time with this mutual friend again and I ask her about it.  After much discussion, she finally admits that she and this other man have talked a lot since our talk and basically have feelings for each other.  I am pretty upset and once again we talk/discuss/fight/argue/cry and she says she's going to call it off with him for now until after we get our things settled.  Then...tonight.  She comes to my house and drops the bomb on me and asks me if I would be okay with her going over to his house because she just can't stand to be away from him.  She also told me that she snuck over there yesterday and met with him and and they both exchanged their feelings that they couldn't stay apart from each other.  I at first am in shock, then I run the gammet of emotions - every one of them.  At this point I am completely devastated and my life feels like it is destroyed.  I tried explaining to her the risks she is taking about bringing another man into this while we are still trying to get things settled and the fact that he has two kids that are also friends with our kids.  I do still love my wife and care about her, but I honestly know that our marriage will not work and I accept that fact.  What destroys me is the fact that she doesn't care what impact this whole thing could have on ending our 16 years of marriage peacefully.  She once again sees me as controlling and not respecting her feelings and not understanding.  All I asked is that she wait until our lives are separated - which we have honestly been working diligently on.  There are just so many details to sort through after 16 years that it just wasn't moving fast enough for her and now she thinks I'm delaying it.  She told me that he and she are just so compatible when the entire time we knew him she told me he drank too much, drives while drunk often and is controlling.  Now that she has that ADHD adrenaline rush going, he's the greatest guy and his problems all disappear in her mind.  I still love and care about my wife and what happens to her and it's very important to us that we end our relationship on a good note.  We have two great kids who are coping well with this situation that she and I will have in common until one or both of us parts from this world and if we can get along and make this as smooth as possible, then it's less problem down the road.  She tells me she can't wait until we're finalized for this man, I tell her I can't be friends with her or be around her at all because she can't even wait for us to be settled before she runs into another man's arms.  I told her to do what she needed to do to be happy, but that we are completely through and that I am not sure I can ever forgive her or this other guy  (who was also my friends) for doing things like they did.  I hugged her for the very last time, told her goodbye, that I loved her and good luck with her life.  As I pulled out of her driveway to go home, she was headed out the driveway in her car to the new man's house.

I know this post seems pointless and rambling....I have so many stories there is just no time to explain anything else, but it's been an endless cycle of agreements followed by disappoints.  I know I've left out a lot of details as well, but there's just so much involved in this that I can't get it all straight in my head and type it coherently.  I am so hurt, disgusted, angry, frustrated and depressed right now that I am honestly numb.  I fly back and forth between every emotion - sometimes in a matter of a few minutes.  I don't know what to do or when to do it other than just get this divorce over as quickly as possible at this point so that I can try to quit hurting and move on with my life.  Does anyone please have any advice or something?  I need to feel something normal again.  

I know I have left most everything out about the kids in this post.  Those are posts for another time.  My head is such a mess right now it hurts to think and dig up these feeling.