My younger sister is my best friend, but she doesn't know.

This is sweet. I'm the very same way with my younger sister, she knows how I regard her and feels the same. We're practically four years apart and have fundamentally different personalities but she makes an honest effort to understand me, as I do her, and we have the best conversations. Our rooms are right next door and we can randomly walk into the other's without fear of being kicked out. She does my makeup, we share clothes and advice, we watch movies and go shopping together, I've tried one of her favorite vegetarian dishes and made her proud. We rarely fight and are quick to make amends. Our relationship wasn't always like this, mind, but it has become so over the last... three? - At least? - years because we've bonded over our strained relationship with our dad (sadly) and I've felt forsaken by my school and childhood friends. (They express no desire to see me and few even speak to me at all these days.) It is sometimes lonely with only one true friend who isn't quite my age, but I've come to accept and embrace that she is the one that matters most. We share blood, many stances on political/social issues, and some of the same pain in our day to day lives. The love is mutual, unconditional and evolving. I've decided she will be my maid of honor in my wedding someday, and the godmother to at least one of my children, and that decision won't be swayed or regretted. I apologize that this comment is lengthy, I'm just pleased to relate so well on this matter. TL;DR: Sisters are a great blessing and we should hold onto them. ♥♥♥

Aw I'm so glad you could relate to this and that your relationship with her has gotten so much better. I'm the same with the school friends, except I'm the one who's been distancing myself...although I feel like I have no other choice? Idk, I'm trying to do what's best for my mental health and remove anymore unnecessary stressors. But that's a daunting path for me so I'm taking it slow. I hope I can get to the embracing stage quickly though, idk why but I'm still to embarrassed to tell my sister. One day though, I guess I have embraced it internally to some extent. I just hope she's not all I have

You don't owe anyone who continually hurts you and makes you unhappy an explanation for your absence, and it is wonderful that you're actively trying to help yourself (and going about it gently), but anyone that you don't want to lose completely, I would let them know. Tell them you need some space for now, but that you will come back eventually and that you'd like for them to still be there when you do because you value their friendship. It doesn't have to be long-winded and sappy, especially if you're uncomfortable with showy affection and/or don't have the energy, but if they're genuinely good to you, they at least deserve to not wonder if they did something wrong. This is how you make sure your sister isn't all you have. And if no one gets it and you do end up losing all the people you hang out with, they weren't true friends and it will be all the more clear who is important in your life. After all, you don't live with the others; you live with her. She sees more of you, good and bad, than they ever could, and she's never stopped loving you. Life is short and crazy, so I hope you do get to a point where you can verbally express how special she is to you while you still have the chance. I wish you well, sweet soul.