I just can't trust my ADD wife of 15 years anymore - is it over for us?

I have been the spouse of just over 15 years to a wife with ADHD.  Like all of the other stories I read, when we dated, all was great.  When we got married it all changed...immediately.  I found out a month after we got married that she had been sleeping with my best friend while we dated and were engaged, and the weeks before we got married, she said she slept with several men to get "it" out of her system.  She had numerous flings during our first 4 years of marriage and now that I look back, I was too young, insecure, and depressed to deal with it.  She promised me (after she was caught each time) that it was anything more than just flirting or just kissing, or the occasional heavy petting but never intercourse.  Any attempts to talk to her ended in her crying, wishing she was dead, shutting me out emotionally, or blaming me for constantly bringing up the past.  All of this is in addition to the constant daily distractions, not completing simple tasks,  not cleaning or cooking (even if I begged or plead), not taking care of the children properly and not even taking care of her own personal hygiene, including her monthly feminine hygiene needs.  I had to take on everything to make a family work.  She would tell me to please be patient with her but never could get past square one. 

She is my wife and the only person who I want to be with for the rest of my life, but as much as I love and miss her now, and need her with me, I can't trust her.  I know of, and she has admitted to, approximately 6 times in the beginning of our marriage alone where her loyalties and affections were aimed at another man over a period of time - usually old classmates or old teenage boyfriends or co-workers, but she chose to stay with me each time (gee, thanks).  I now know that those were behaviors brought on by the symptoms of ADHD - that need for attention and stimulation but it still hurts badly.  I went through years of thinking it was me - that I was doing something wrong.  I blamed myself a lot.  She always said that I had not done anything emotionally, physically, or financially to cause her to look elsewhere.  I am confident in my abilities to provide for her and to satisfy her sexually, and she claims that she only wants to be with me intimately, but if sex is the only part of the marriage that actually works - at some point even that's not enough to sustain true happiness and I feel guilty that this is all that we can do together now.  She was diagnosed with adult ADD a few years ago and has been on and off of medication.  Even when she took meds she changed for a minute and then reverted back to her old habits.  Her self esteem is lower each year than before and I can't risk losing the confidence I building in myself to try to raise our daughters.  

I have noticed lately there have been two Facebook relationships in the past year - those who have experienced this know exactly what I'm talking about - she accidentally leaves her page logged in and there all these messages from guys and her flirting back and forth.  I am now just getting over the past hurts from over 8 years ago.  After finding out about the last one I decided that we had to live in two different houses, so she is living with her parents.  I am trying to keep our daughters on the regular routine as much as possible in our home. Her mother seems to do everything for them when they visit (cook, clean, clothing, etc) and my wife is showing little signs of improvement - and they see for themselves now that she is very distracted and unable to complete simple tasks in the midst of this crisis.  I am sensitive to my wife's problems and it hurts me to see her cry for me and the children and tell me how much she loves us, but after the tears are dried, she goes directly to sleep, goes directly to eat, looks blindly at TV, or surfs the net for hours into the night and she can't find the motivation to really start change.  This has gone on for over 15 years.  She can't hold down a job because either she quits, gets fired, or battles the urge to be the "buddy" and not concentrate on getting the job done.  I am mentally exhausted and wondering if it will ever get any better. 

I can live with my wife having ADHD (for better or worse, in sickness and in health), but these symptoms of ADHD lead to her need for attention and she says that she has issues with separating platonic relationships from infatuations and affection.  She told me that she was molested as a child, and is scared to even talk about it all these years later.  I don't know by whom (I think it is a family member and he still coming around now) or how long it took place.  All I know is that the ADHD has led to behaviors that have weakened my marriage.  Am I fighting a lost cause by trying to help her through this?  She has agreed to see a psychiatrist.  Should I give this one more try.  What if it happens again?