What grief/pain does George have to deal with as a result of sacrifices made by Lennie?
(Lennie's sacrifices would include how he often gives up what he wants for Georges sake -such as talking to Curly's wife and petting mice- and what else?)
Is this an assigned question? I wouldn't consider the things you mentioned actual sacrifices made by Lennie since he doesn't give them up willfully and in the spirit of renouncement. He is simply 'minding George,' much as a disgruntled child would obey a strict parent.
Remember that because of Lennie' mental handicap, the relationship he has with George is not horizontal but vertical. He looks up to George as a father, big brother, and nurturer since he would be "lost" without him. As for George, he resents the ties that bind him to Lennie at times, and then feels guilty about it. He has known Lennie since childhood, having promised to look after his friend to Lennie's Aunt Clara, the only remaining family member Lennie had left. Now that she is gone, he must assume that responsibility. George's relationship with Lennie is one of friendship, true, but it is also one of moral obligation.