how to tell my mom politely?

I moved country just over a year ago and have been home once due to the fact of changing jobs/moving house and the flights are too expensive! When I lived at home my step dad was always drunk and drinking which resulted in me having to live with my grandparents until they passed away then I'd no other choice to move back home at the time. I was sat in my bedroom for 4-5 days in a row because he would drink from morning to night and my mom always sided with him even when I asked her to put him out after he went to hi  me and accused me of being on drugs. He's really sweet when he's not drunk and would give me anything to help me out. Her and him want to come visit me but I'm uncomfortable with it because I know he will get drunk and show me up in front of my partner and the town I live in is small so with different accents it's not hard to guess it's my relation and ruin her time away. I have said about coming alone and she won't so I decided me and my partner would go home for a few days and we would stay with my aunt because he ruined my time home the last time (4 days at home and he was dunk the 2) plus her house isnt overly clean and then she refused to pay my flights and told me I was a horrible horrible girl and really hurt her. I love her to pieces but I just don't get why she's trying to make me feel bad when she took a mans side over her daughter. Is there any ways I can get her to see my side or should I just tell her how it is?