Anyone else's sister/family member make you do this?

I'm 18 and my sister is 21! She's had a FWB for over 4 years who she's been in love with before they came into this type of relationship! He puts himself on dating sites, talks to other women and he just doesn't care about her and it's all about sex for him while she's in love! She got off Birth Control and I personally know that she wants a baby(she told me) and I don't think she realizes how much of a fucked situation she would be having a baby with someone like him! Every time she has a pregnancy 'scare' she's making me go buy her pregnancy tests like I wouldn't mind if it was for myself but she can't buy her own and she's 21! She gives me the money and tries to make me go in! She's 2 days late today and every time she's just a day late she's running for a pregnancy test(I know she's hoping she's pregnant! Anyone else's friend, sister or family member like this?? Ugh