Vicious Circle

I am brand new here - I have been married for 18 years - I love my wife - we have 2 wonderful kids but it is very very hard on me, at times, because of my wife and her "conditions". She had been professionally diagnosed as having a General Anxiety Disorder and recently her therapist brought up that she has many ADHD habits as well. I read the NY Times article about this subject and was fascinated by it because there were about SEVEN things in the article that were dead-on for me. And I try and carry the ball and be sensitive to her condition but at times, the anxiety, the fear, the forgetfullness - it just is the large gorilla in the corner of the room and it takes up all the energy and oxygen and not much is left over -certainly nothing is left over for me. I have always been low maintenance in my life - but obviously everyone has times where they need to be helped out, they need support but most of the time we are just dealing with my wife and her issues and yes, over time, it builds up resentment and anger. That is what usually creates the true friction - in that 9 out of 10 times, I will be understanding and help soothe her and know that she is having anxiety and can't help it. But I am only human and if I myself have had a crap day and am tired and I snap and don't show patience - well, then it's always like "well, what's YOUR problem?" And that just isn't right. Relationships are hard enough but when you have to put all this time and energy into someone else's fears and anxiety - well, it just drains you. I do not mean to come on here and just complain and yet I also feel it is helpful to be able to come to forum like this and read of other's experiences - good and bad. Thank you.