Sister isn't speaking with me anymore and I don't know why

I know as a 31-year-old woman I should understand that as we get older people have their own things going on and might not always communicate back. But my sister has not responded to any of my text messages or calls in the last 4 months. No Merry Christmas, no happy birthday... Nothing. Sister and I grew up in a home where there was nothing but neglect and abuse the whole time we were there. So my sister is really the only person that understands why I am the way I am and I don't feel like I have to explain myself to her. Last time I texted her was last month. I let her know I will I'm always here for her no matter what. This was my best friend and now it feels like she's just disappeared. I don't have other people that WANT to be around so how do I get over this 💔