O.K I know there are many people who don't get on with their loved ones parent(s)/family... but this is really affecting me and making me depression so much worse.

My boyfriends mother is an alcoholic (has been since before I knew him), she's never thought she's a alcoholic though but has recently gone to rehab (I don't know a lot but apparently she still doesn't believe she's an alcoholic and is causing a little bit of trouble). I've always kept my views of her open, when she's sober she is a lovely person but a couple of months or so ago she turned on me. She shouted and yelled at me, including telling me that I'm ruining her son's life and she doesn't want me to be with him. She's also told me that I 'simply have to get better' (I've been an outpatient at hospital for two years, they're unsure what I had and how to tackle it and this all contributed to my depression so the comment didn't go down well with me and hurt).
I know she's 'ill' and I shouldn't take stuff to heart, but I think she's depressed too and just wants her son and gets upset when I'm with him (we're in a long distance relationship).
I know it sounds weird but I keep having nightmares about his mum, chasing me and damaging my possessions and keeping me away from her son.
I love my boyfriend to bits (there's no way I can tell him about the dreams and I don't really want to tell him how I feel about his mum, I don't dislike her, I'm just very upset that I'm not accepted by her). The problems with his mum just adds to the long list of my problems and my boyfriends. It's really starting to affect us now. I'm unsure if there'll be any way around it and it hurts me a lot.
My main problem is not being able to talk to my boyfriend about it. After all, she is his mum and he misses the sober her... I don't want him to think that I hate her because I don't.
Has anyone had similar experience and coped better than I'm doing?

I'm at a loss... I've got too many things to think about (besides this), I'm only young I'm meant to be enjoying my life

Molly