What link George to Lennie?

Because of Lennie's simple mind, when Lennie's aunt passed away George promised to look after him and so when ever Lennie gets in trouble George has to help him get out of it. And also when they first come to work at the ranch the boss asks George who Lennie is to him he says hes his cousin. George mainly started looking after Lennie was when they were young George asked Lennie to jump into the river as a joke and he did. George didn't know he would and Lennie couldn't swim either so he had to go save him. from then on he never joked around like that with Lennie again. So not only they are companions but they pretty much family now.