should i cut her off?

okay me and my sister always had the best bond growing up we were basically unstoppable when we hung out together but lately looking back on some things had made me question if shes a secret backstabber okay so i got my first BF last year and when i brought him home to meet my family my sister gave him the meanest look and a short Hi and walked away ..kinda weird because she only acts like that around people she has a crush on but i ignored it anyways fast forward a month into the relationship she always wanted to hang out with 'me' when my boyfriend was over and it was weird because everytime she walked in my boyfriend would go silent and they would just talk to eachother like short replies i felt like i was the 3rd wheel everytime we all 3 hung out and then eventually towards the 3rd month they started laughing together but my sister was laughing laughing iykwim and everytime me and my bf had an argument her advice was 'break up with him' i thought she just secretly hated him but fast forward a week or two after the break up she admits to me she wanted to fck him the whole time but she 'lost feelings' for him after we broke up please lmk if i should cut her off or not i only kept her around because i have 0 friend hmu!!!!