Why doesn't my fiances mother like me when I did nothing wrong?

I just got engaged a month and a half ago to the man I absolutely adore, and I couldn't be happier. We have been together 4 years and 3 months; friends for over a year. His mother is an alcoholic although she doesn't want to realize it, and lives by herself and has been since he was born; he's an only child too. He hasn't lived at home for two and a half years. In the first year, things with us were great but she got mad drunk one night, hollered at me for no reason and he stood up for me, and he moved out because that was enough; you can't live with someone like that if you can help it! Long story short, that same night she tore up his room by ripping up my pictures and throwing the frames at the wall breaking the frames, while also leaving a few holes in the wall. He went to get his things the next day while she was at work, and found his room in a "rip everything of the girlfriend up". She also blamed it on me! How nice? Anyway, I just wanted to show an example of how she already is. But she ADORES her son. Not very fond of me and doesn't try to talk to me, and when she does, she complains and bitches about everything. Worries about the worst-case scenario, and nothing he and I do together is good enough and she makes us doubt everything we're deciding on if we try and share it with her. I feel like he just condones her behavior, and no one in the immediate family tries to get her help. She's sweet as pie to her family but very rude to me and says I never go over anymore..He is 25, I am almost 22..we are trying to build a house, plan a wedding, I'm graduating, just started a new job, and he's gone Monday-Friday..HELLO?! I don't have time for me! and she just blows that off like I don't have enough on my plate. I feel like she does it to make me feel guilty and she tries to find reasons to be mad at me. He told me the other day he just doesn't feel like dealing with her when she's like that. Well, if you don't want to with your mom, why would you with me?! What if I'm down in the dumps one day and need someone to just even bitch too about everything bitchable!? lol but seriously, you've got to support the ones you love, so why won't they? Anyway, she has a drinking problem as you already know, and I can't keep putting up with her making me feel like I'm not a part of anything. And I think he may be telling her things about our personal business, like him helping pay for my school tuition although, I paid him back within a month! and it wasn't but only $900. I am graduating this semester and he only helped with two. We are getting married, that's what support is! Isn't it?! She brought it up tonight at her house and I told her I paid him back, but how would she know that unless he was telling her? He is a really great guy. We've had our ups and downs, but who hasn't? We've worked through it, but this really hurts because what if he's telling her things untruthful to make himself look good?! and for what? I haven't confronted him yet because I feel like he will try and deny it. We've been so great this week. I don't know about that family sometimes..someone please help and tell me if you think he is hiding something from me? Or is it his family influencing him? She's even turned his grandparents against me because she goes over and feeds them untruthful BS; and they believe it! Although, if you know me, you would know I'm not that kind of person. I want peace. I just don't know what to do anymore...any real advice is greatly wanted