How do I deal with the constant negativity?

I am new to this forum. When I read so many of the posts, I felt a lot of relief. It was as if I was reading a mirror image of our life.  What I don't understand is why people with ADD or ADHD can't see the havoc they are causing.  The tension in our house is ridiculous. He is terrible at doing household chores and admittedly I am worn to the nub. The frustration level with my spouse is hitting an all time high. Tempers are flaring. My parents, who live with us due to my Mother's disability, are fed up with his behaviour. They are ready to sell the house and go our separate ways just to be rid of seeing him and how he speaks to me.  When I confront him with how he speaks to me, others, his seeming inability to take up his responsibilities as a husband, father and homeowner, he just throws it back at me.  He cannot take any amount of criticism. No matter what I say or how I say it is wrong.

He is also the most negative person lately. He always has been a little dark and negative, but it just seems to be getting worse. When our son, who is almost 2, get tired and cranky and wants his daddy, instead of soft, soothing tones, all I hear is Why can't you just go to sleep. Always negative. I have my days like that, but this is all the time with him. Never a night different. I try to do it all, but I can't. I am one person. I feel like the weight of everything is on me. I can't trust him to look after our son, who is extremely active and into everything and a climber. Many times I have caught him watching t.v or playing a video game and igonoring our son. When I catch him, our son is usually crying or getting into something he shouldn't.  I have the right to be able to have some me time. I need to get a part time job and I am utterly afraid to as I know the house will fall apart. My husband simply can't be trusted to look after things properly.  He has yet to be officially diagnosed with ADD but I am sure that is what he is suffering from. A previous psychiatrist felt that is what he had, but all he did was push pills and never actually sat and talked with my husband.

I am frustrated beyond belief. I love him dearly. He really is a decent guy. But I am not sure how much more I can take of the messiness, not helping, bad manners and behaviour, etc. It is wearing on me. I feel like I am mother to both my son and husband. No one feels they can talk to him. So everyone come to me and vents on me.  I get it all.He gets nothing.

Am I wrong to feel this way.

any advice would be great as right now it feels like the house, our family and our marriage is spinning out of control.