AIO- my boyfriends sister makes me feel kinda weird

Ever since we started dating, his sister (F17) made it clear that she was threatened by our relationship because they grew up together. she'll post/say how my (F19) relationship with her brother (M25) ruined her life because of how we started dating which i will admit was not an ideal way to meet. but we love each other. i think his sister feels replaced but i dont know what to do about that, she never gives us any privacy and is constantly prying on both of our social medias. my bf and I got into an argument with each other about setting boundaries with her and he told my friend that it seems like im jealous of his relationship with his family but im not. i just wish there could be a separation between family and significant other until we get married and im officially apart of him. i dont want him to take it the wrong way if i tell him i want her to give us space. he has had multiple talks with her about minding her own business but its only a matter of time before shes posting shady stuff again or saying weird things😭.. idk what to do anymore. the screenshots above are just SOME of the things shes texted me/posted. there are so much more. idk if im overreacting tho because i could be and maybe im getting in my own head. when i see him again next year, im scared shes gonna take all of our time together alone and make him feel bad for not hanging out with her.. which she has done multiple times. my bf is mildly autistic so he tends to feel guilty easily and ends up feeling like a bad brother but he isnt. could there be a reason his sister is so involved in what he does even though they're 8 years apart? i wouldnt understand because idc what my brothers do, but she really does. can you all give me advice or maybe explain why this is happening and what i should do??