Please Tell Me Am I A Nasty Person For This?

HOw do i stop turning bitter. I always hated bitter people and i fear i am turning into one. I believe you make your own luck to a certain extent but lately i feel everything has come against me. My main prob is my mother who is 70, she is mentally ill and obsessed with me, she feels 100% its my job to come live with her, forget my partner and ‘look after her’. Everyday i battle and say no, i put up with temper tantrums and threats. She is under psychriatic care. Shes fully functioning, she drives. My dad lives 10 miles away from her but makes sure shes looked after finanically and practially and stays with her at night. But he ‘expects me to chip in’. I live with a constant pervading guilt that wreaks my life. I do as much as i can i phone her 3 times per day, i viist her for a full weekend every 3 weeks and all holidays and xmas and easter. I hate it but i do it ‘out of duty’ no more and the resentment is fierce sometimes as i feel i am sacrificing my own happiness, yet if i dont do these things i feel so guilty.
I moved cities with my parnter who had a specialist job. I told him to move here and he gave in after 4 years. Hes lost his job and now we are both stuck somewhere we dont want to be and both very unhappy this past 2 years. I’m bullied at work but there are no other jobs in this city. We haveent got on teh property ladder, his is 46, i am 31. I love him very much and he is very good to me, i want ot spend my life with him.
Meanwhile my best friend has climbed the career ladder adn i am HONestly very pleased for her. I’ve always encouraged her and told her how proud i am of her, which i am. She had a very difficult life and deserves this sucess. We were always a support for each other, we know each other since 5 years of age. But she always critisced how i handled my mom. I know its not perffect, but i do the best i can, balancing it all and livign away from it so i can have some peace and normality. I’ve always been there for her when she was down in the crap and she came lived with me 3 times in a city i lived in but on each occasion gave up the job and moved back to her parents. I never had that net. I’ve kept going throuhg some horrendous jobs just to keep a roof over my head. Yet she doles out advice and says i’m too much of a chicken with my mom.
My moms family have cut her out. They live hearby and never visit her. Shes been abusive to them and they wont take it. Yet, they watn me to be friends to them without her. I’ve deciced they support me in this situation or i cut them off, and i’ve cut them off. They used to ring me and tell me all the nasty things she’d say aobut me even though i didnt want to hear it and they would give out to me if she rocked up at their gatherings uninvited although i woudlnt want her to be at them and i’d tell her not to go that she wasnt wanted. Am i wrong to cut these relatives out? I’m 31 and have no siblings…am i turnign into a nasty person?