Help! Husband defends his mother after her rude remarks on facebook. Am I wrong?

I've been with my husband for 5 and 1/2 years now and we have a good relationship. The problem is his mother and is on the brink of destroying our marriage. A little background, I initially got along with the woman. I found her a little annoying and intrusive at first but I was able to dismiss it uming that it was her way of getting to know me. As the relationship continued she became more aggressive with her questioning and was now telling me how I should and what I should do. When we were married she didn't congratulate us or say a word about it. (We had a little court wedding) She was more concerned with his son's box of Easter candy than anything else. While visiting she has made comments about how our house is cleaned, how we cook, and to how I interact with his son. All this she says to her husband in a voice loud enough for me to hear. Again, I gave my husband the respect and not respond to her remarks and that took A LOT from me. He always says she means no harm and that she doesn't realize what she says. He has also blamed it on her liver transplant she had 10 years ago! I didn't know it was a lobotomy! So I have kept my distance from and just left the talking between her and her son. This time she crossed the line. She posted on Facebook that I was a sissy because I can't cope with 115 degree heat and that she wishes that him and his son's mother were still together. This was told to the ex's mother on Facebook for the world to see. She maintains a VERY close relationship with the ex, her mother and her grandmother. But when they were together, my husband and his ex, his mother couldn't stand any of them and always talked bad about them when we were first dating and well into our 3rd year of marriage. I asked my husband to confront her regarding the FB comments and he did. All he did was mention it to her and she said sorry and that she said it because she felt closer to his ex than me.I said that was a lie and that there were underlying reasons, mainly the relationship with his son and I WHICH my husband and I have an understanding between us and have worked things out. I told him that I do not want her staying at our house for two weeks during the holidays. That set him off and he said that he has to look out for his mother and our daughter now. That he can not deal with the issues between me and his mother and that he doesn't want to. He basically said he chooses his mother over me and our marriage. I was hurt, angry and devastated. Am I wrong for feeling that way? I just want to leave at this point and let him, his mother and his ex to work things out and try and get back together.