Please help feeling devastated & so confused :(

Hi everyone :) I have been what I thought was happily married since I was 22 (but together since 19) and I have just turned 45. We have 2 beautiful children my son whom is turning 18 in March (and has been diagnosed as a mild to moderate sufferer of adhd) and my gorgeous girl who will be 14 in July. My husband was diagnosed with ADHD about 14 years ago now but he had always led me to believe that his "symptoms" were minor & the need for treatment was non-existent. Through a bad feeling about something I discovered a few months ago that he had made inappropriate advances towards my sister law and if that wasn't enough sent approximately 10 sexually SMS   messages to my step mother roughly about 5 years ago.  Now as I am very close to my family the discomfort that it   has created has been devastating for me and created rifts   that I sometimes fear are beyond repair . Once I  discovered the inappropriate advances he volunteered the  information on my step mother, but to be honest I feel this  was only through fear that it would be revealed to me my family with them now being aware of my knowledge of the  indiscretion. I was devastated and felt betrayed on all  levels at him for his behavior and also at my family for  keeping this knowledge a secret from me for so many    years. This all occurred only a few months ago and I have been struggling to come to terms with it all still. To his  credit he immediately sort treatment and is now on   dexiamphetamines and seeing 2 psychs. At the time  when I learned of his dirty little secrets I foolishly believed  him that he had never been unfaithfful in all of the years of  our marriage but tonight he came clean (after previously  telling me time and time again that I now knew everything)                     that over the years of our marriage he has been unfaithful  dozens and dozens of times with prostitutes. He was sexually abused as a child & i have learned from studies on the link between adult adhd sufferers who were sexually abused as young children & sex addiction. Although i cant remember the exact percentage it was some staggering figure like 97% of these people who were abused as kids & had adhd were found to be sex addicts in this particular study that i have read. Part of me is  saying what the hell are you doing still laying here beside  him but the bigger part still believes there is hope. I love  him to death even though I feel like I had already been to  hell and back over other issues and sacrifices & I am  feeling like I'm only just barely capable of breathing at the  moment. Am I crazy to do this & believe him when he  says he is now ready to face all of his wrong doings and  do whatever & take whatever treatment or medication to  keep me. He told me that it is only because of his love for   me that he came clean and that he was sick of the guilt  and lying to me.i so want this to be possible for a happy  ending but I am so scared I feel sick! He states that his  behavior suddenly ceased a year ago although he doesn't  know why& that because it had stopped and through  seeing  the required specialists found the courage to tell me. He  also said that he had no control over this behavior I the  past and that it always made him feel sick afterwards,  what I find the hardest thing to understand is that if he  was so "out of control" for so long why the hell did he not  get help years ago? I suppose I'm afraid that he may  have just wanted to have his cake and eat it too and is  just using the ADHD & sex addiction as an excuse:(  just so you know it is  not like I have been prudish sexually with him throughout  our marriage, on the contrary I feel like I sold my soul to  the devil in order to keep my man happy, or so I thought,  now I just feel used and like a complete and utter fool for. being so blind for so long. I would really appreciate any  advice from you all from both sides of the fence if  possible. I have already been to the darkest of places &  felt like checking out of life completely ( I took a  dangerous amount of prescribed synthetic morphine &  alcohol) only just the other week so I'm feeling very alone  scared & vulnerable & would love to hear your thoughts,  I have read that in part of the healing process it is essential for him to be openly accountable with everything for the other spouse to regain trust. Although he says that he is prepared to do whatever it takes to save what I blissfully unaware thought was our happy marriage yet he already got defensive & had an angry tone for me just checking his phone and asking questions about phone numbers dial led. If he is serious about doing anything and everything am I unreasonable in expecting him to do this without him trying to make me feel as though I have done something wrong just for asking ?  thanks in advance & I'm sorry if I have written too much I just wanted everyone to have a clear understanding so that in turn I could maybe get some good advice from those who have been there already. :/. Xxx