Had it - separating - can't take the lying.

Hello - I am new to this forum and very grateful that it exists !   Brief as possible, my story:  I am 59 married to a 61 year old man for about 3 years together 7 years.  About a year after I inherited some money, my husband just stopped working.  He works freelance from home, and he just stopped.  Since then we have gone through much of my inherited money (I bought us a house and furnished it) because he has NO income.  On top of this I discovered that he had lied to me about his finances before we married,as I asked for full financial disclosure.  He lied, saying all was okay, but he has not paid his business tax in 5 years, amounting to $20,000 owed and I found out about it by chance when a cheque bounced due to the government having taken money from his bank account.  He never would have told me, he admits this.  

He lies chronically and tells me that lying is "part of every marriage and you are too uptight about it".  

At first I tried to help him change, got him to a psychiatrist a year ago, who diagnosed ADHD right away, got him on Concerta for ADHD, Wellbutrin for depression,  and to a cognitive behavioural therapy group, which he attended for 16 weeks.  I got all the Hallowell and Rady books on ADHD, read everything, supported him, but after the group was over, he dumped almost everything he had learned and went back to being the way he is, despite weekly couple counselling.   My husband uses the diagnosis as an excuse for all his lousy behaviours and just last night told me "You re treating me like a bad person, instead of a person needing understanding" - this is what he came up with after reading a couple of articles from this site.  BUT HE BEHAVES LIKE A BAD PERSON - this is the dilemma I see in many of the posts here.  How on earth is the non-ADHD spouse supposed to cope when the ADHD person JUSTIFIES all the rotten stuff they do "because I have ADHD?"     I have done everything I can think of, and am giving up, separating from him.  I feel guilty about it, because it means he will be very poor, likely end up on welfare, but if I don't leave him, he will break me.  I don't work anymore (I inherited enough not to have to work anymore) but if this goes on, I will have to seek work again, and my health won't permit that.   It is all so sad, and so unnecessary, but at 61 years old, I doubt he will change.  I will miss many of his qualities, but my own self-esteem is hitting the floor, and I am becoming isolated because I do not want to talk about this to my friends - if they knew he is such a liar they would be shocked.

So here is my question for any of you who may care to respond:  How can the ADHD person justify lying, and expect CONTINUAL forgiveness for lying ?  How do they not see themseThankslves as subject to the same moral code as the rest of us ?