3 year old with asd diagnosis

hi, this is the first time I have ever done anything like this but feel the need to reach out to anyone that could give advice, or just show a little understanding. My son was diagnosed three months ago and although I feel that I've accepted it, i can't say the same for my partner. He says all the right things to other people but when it comes down to coping with our son on a day to day basis, he just isn't getting it. I think he knows deep down that he's not dealing with things the way he should and is taking his frustrations out on me. I try to talk to him but instead of listening he turns everything I say into a critisism. He is so negative towards our son, yet our six year old daughter can do no wrong in his eyes. I am at the point of leaving, even though it is the last thing I would ever want to do. How can I do the right thing for both children?