According to E!,
…a family source tells E! News that [Kylie and Tyga are] not a couple.
However, while the insider says they’re just friends, another source tells E! News that things have taken a romantic turn between the two. “Tyga and Kylie Jenner have been seeing each other for a few months now. What he likes most about her is that she is a very loyal friend first and foremost and easy to be around. He gets along with her family very well.”