Why is the nicest people gets treat like....

To me, I'm one of the nicest person to know but why is it the nicest person like myself gets treated like shit? Like theres a saying, "Bad things always happens to good people." I mean why is that? I do get it but I just don't freaking get it at all. I get the concept when someone who is the nicest gets taken advantage of. I mean I get the whole thing but I just don't get it anymore. How can the nicest person make enimies? I just don't get it. You wanna to get alone with everyone and accept for who they are and like people but you yourself has enimies as well. I learn from the bible that you can have your friends but keep your enemy closer. I can be nice to the worst enemies of t he earth. How is it like the nicest person do things for others and are loyal and respectful to others when those don't turn the favor. I just don't get it no more. I saw a trailer of Cinderella where her dying mother tells her that "Always be nice and be kind even if those who treats you terribly but you're the nicest to your finger tips. When your kindness takes action so there'll be magic, " I think its how it goes but there's no magic here but miracles. To be honest I'm happy about the engagement. What I'm not happy about is how I was being treated at work and how others treats me and it makes me sick. My fiance and I went for a nice dinner last night and as I just open a gift and saw a beautiful bracelet then I receive a awful text and I shown little burst in tears my fiance ask me what was wrong and I felt sick to my gut and showed him and I walked out the table saying, "I'm sick and tired of it." He went to ask me why and I said, "I'm tired of everyone treating me like crap. Why there are others who are so mean for no reason?" The message I ireceived was in fact my fiance's mom. I told him how I feel since she ruin my night and appetite. I told him why she turned into my enemy all of a sudden after when I thought she was very nice to me? Ever since my sis came over she's been nothing but saying things behind my back and making my life miserable now she's piss at me cause I can't go to school now and its not my fault. She hates me for no reason and im getting the impression of it. I know they say don't let her get into me but she does and hits hitting me badly. She thinks I have been ignoring her when she has been ignoring me and not trusting me and I don't ask much. Is there so much to ask? Just because I'm trying to do things to help myself why someone getting angry for not texting them back right away? I always answer back as soon as I can. But I told my fiance if she wants to act this way to me then I'm leaving and moving somewhere else cause I'm done with peoples crap. I told my fiance if he wants to leave he could I can't force him cause were not married. I can't make him stop having relationships with his mom. With me I guess I'm done with her once I leave but yet I'm in love with her son. What can I do? I can't stop him for caring for his mom. I mean I do care it just I can't handle the pressure no more. I hope when I make that goal all this stress will go away for good.