Girls need your opinion

So i’ve been with my boyfriend for over a year and there is always problems between us because of a girl that he talks with (she’s his cousin but there was a little thing between them before we started dating ... and that’s what makes me upset when he talks with her...) so i found pictures of her on his phone (she sent them to him) i asked him to delete them but he didn’t want to... doesn’t it mean that he cares more about her and not me? Doesn’t it mean that he doesn’t care fore our relationship? Am i the only one who finds this wrong? Because really it’s driving me crazy he’s blaming it on me and saying that because it’s his cousin i don’t have the right to tell him to delete her pictures...