Why did some people get me wrong when i try to help or be nice with them?

i got two unofficial,somehow related family..they are girls and at the first place,both of them wanted to take me as their brother since that they had no elder brother..after a long time,when we try to be close with each other,some problems occur,and that makes our relation become worst..they get me wrong,even their boyfriends,their boyfriends thought that i'm the one who ruined their relationship with their girlfriends,i try to treat them as my sisters,i try to be nice with them,nothing more than that..that's makes me a bit sad and disappointing,until now i still wondering,what had i done?