In the book Of Mice and Men, why did George quit teasing Lennie?

We see George reveal his compassion to Lennie when he
speaks with Slim about their circumstances in chapter 3. From that point on out, George
remains in defensive mode for Lennie. George cares about Lennie and cares like family.
In families, it's okay for members of the family to pick on each other,
but, and most importantly, others on
the outside are not allowed to pick on family members. George remains in a defensive
mode from the time they arrive on the ranch until the end. From there on out, George is
protecting Lennie by dictating what Lennie can and cannot do and say. When push comes to
shove at the end, George prefers to ensure that Lennie's death is comfortable as opposed
to torturous. When George moves into this defensive mode, I think his
entire capacity to tease Lennie leaves him.