I just have to get this off my chest

my older sister had a son at 19 and was with an abusive pos. she stayed with him for four years and during that time she mostly had her son all the time like a normal mother. skip to when he was three years old she left him and then she went back wild. Going out every Friday and Saturday leaving her son with me and my mom (we also had him three times a week). then she went dated multiple guys(not at the same time) getting her son attached to every single one of them and getting his heart broken every time. leaving US to help him deal with his broken heart ( his thought his dad died multiple times bc his dad never called or anything so he has basically no father figure at all). anyways he is ten years old now and basically lives with us and not his mom. and she acts like she is the best freaking mom on the planet. she gets him maybe two times a week and that is us making him go to his mom's house. he hates it over there and I don't blame him. she expects him to act like an adult HE IS TEN! And she posts to fb about their "great times" like she is fb mom of the year. oh and I forgot to mention her current bf has a daughter that she treats better than him. she spends most of her time being fake with the daughters mom so she can get close to the little girl. I am not saying she shouldn't get close to her but at least treat your son with more care and love than someone who isn't even yours. and she is delusional if she thinks she is getting custody of the little girl so they can be a "big happy family" she is fake it angers me to no end bc it is not fair to her son. and I also resent her for me having to grow up faster to take care of her son. and it just about KILLS her to give us money for his school fees and he is in karate so she pitches a fit that she has to pay for the supplies and equipment. it also makes me mad for my mom bc she isn't a grandma she is another mom but I can't wait to have a kid so she can know what it's like to be a GRANDMA instead of raising another kid. sorry this is so long I couldn't stop typing. this has been on my mind for a while. and this might so horrible but I'm glad she can't have another kid bc I'm scared she'll shut out her son even more