Why did George shoot Lennie?

 In Of Mice and Men, George in Lennie fall in love with a dream they have--a dream to one day become financially independent and run their own peace of land. Their captivation with their dream is great, and they begin pooling together money and making plans. Their plan is beautiful and exciting, but one that is never achieved. It is a plan that George is forced to suddenly and unhesitatingly sacrifice after coming so dramatically close to achieving, when he shoots Lennie in the head.

He shoots Lennie, his beloved companion, who like a child, gave him a sense of responsibility and purpose. As George himself often says in frustration to Lennie, his responsibility for Lennie is the reason that he forsakes other pleasures. Caring for Lennie is a responsibility left behind to George by Lennie's aunt, and it is a responsibility that George takes upon his shoulder and faithfully executes by saving Lennie from predicaments, guiding and instructing him, and not leaving the side of Lennie.

Lennie is a burden to George. But I don't think that's the reason why George shoots Lennie. George loves Lennie too much. It was at the peak of George's excitement and preparation to buy the new land and finally actualize their goal when he his forced to, all at once, by the whim of God or nature, give up part of his dream. George had imagined a pristine and happy future for himself; he had set forth a difficult, yet beautiful goal to work towards. And he had worked towards it. A dream and goal he and Lennie had set forth for a long period of time, and toiled under the hopes of achieving. The very source of determination of George pushing him to keep working, and a palace of wonder, ever growing under the nourishment of imagination and dreams.

But randomly, unexpectedly, and devastatingly, the foundation of their goal is wrecked and comes crashing down, as if it were nothing more than a mouse's carefully built home, accidentally destroyed by a reckless hand. As if it were a elaborately constructed hummingbird's nest, carelessly ripped apart by the hands of a curious child.

When George reaches the cusp of achieving what he had worked so hard towards achieving, it is taken from him. Lennie is taken from him.

But why was George forced to give up Lennie? Was there no hope of escaping the ranch and away from the mob trying to lynch Lennie? Why could their dream not continue? Lennie, too, had recklessly sinned repeatedly, most recently by killing Curley's wife. Playing with her hair, that's all. And snapping her neck. Could that sin not be forgiven?

Earlier in the novella, Candy's sick, old dog is taken from him. Candy could have probably saved the dog if he wanted to, but passively allows the other men to shoot the dog. Candy does not have to shoot his beloved, long-term attachment. But George does. George has to raise his own hand to shoot his companion. Was this sacrifice demanded of George, in the same way it was demanded of Abraham to kill his son?

So many unanswered questions.