Backstory as follows as short as I can make it.
DSis and I are close, always have been due to a sometimes difficult, emotionally stressful childhood with a DF that drank too much and a DM that enabled him and put him first all the time for an easy life.
6 years ago DF died and we all sighed with relief but even though we were glad he was at rest from his inner demons DSis and I struggled badly with the grief - it was a lot to work out in our heads.
Within a few weeks of his death we found out DM had been having an affair though which hurt so much it felt almost physical. True to form DM put the new guy first yet again and moved him in within a few months. I was already married with children but DSis still lived at home. DM immediately started putting pressure on DSis to move out as her new partner made it quite clear both myself and DSis were too close to our mother and was quite jealous. DM took this as a sign of his great love for her and would not listen to us when we pleaded with her to protect herself both financially and emotionally.
If anything, us trying to advise her angered her and her and I had a huge row as I’d said I didn’t trust the motives of her new partner (he moved in as soon as he could, installed both his children in his houses he owned and insisted my Sister move out).
My sister was heartbroken as was I and communications broke down between me and my mother back then as she decided she didn’t want anything to do with me. I was the ‘spokesperson’ for myself and my younger sister who was as devastated as I was but DM decided to cut me out and go NC altogether.
The relationship between my sister and DM continued albeit it was very strained but DSis eventually managed to find a place to rent and DM paid for some white goods for her. My DM’s mother (our gran) is still alive and she intervened and also told DM she was being cruel and it was all so fast and DM cut her out too.
Thing is, DSis has continued this relationship with our mother, in fact getting closer to her over the past few years and this makes me so angry. I spoke up for both myself and Sis and my family and Gran have been cut out yet DSis is quite pally now! Where’s the loyalty? Sis was happy for me and our gran to stick up for her when she needed it and now she’s gone back to the person who kicked us both when we were down!
I can’t help but feel betrayed but don’t want to spoil my relationship with my sis as I love her. This is typical of the golden child / scapegoat scenario of when we were kids all over again.
How do I even deal with the anger that this causes me without ruining my relationship with my sister?