For Lennie, he often sacrifices what he wants to do for George's sake. While George is not trying to be mean to Lennie by asking him to give up mice or conversation (talking to Curley's Wife), he knows that he must protect Lennie. While Lennie doesn't always obey George, he is willing (most of the time) to give up what he wants to do in order for George and him to stay together. Lennie does this because he truly cares about George. In Chapter 1 he offers to give up his food for George--a seemingly simple offer, but during the Great Depression, it is a true sacrifice.
George consciously makes more sacrifices for Lennie than Lennie is capable of making. He sacrifices stability because Lennie often does something which forces George and Lennie to flee. George does receive Lennie's unconditional trust and love because of his loyalty, but he must still sacrifice much in order to take care of Lennie. The end of the novel is the best example of sacrifice on George's part. By shooting Lennie, George knows that he is saving Lennie from a cruel fate from Curley, but he also knows that he is sacrifice his sanity. His choice is painful and conflicted, but he demonstrates his love for Lennie by doing what he thinks is best for his friend and not doing what would be easiest for himself.
If you look at George and Lennie's relationship as a parent-child relationship, you will see the true sacrifice and love on the part of both characters. It is difficult for parents to discipline their children, but they do so in the hopes of helping their children develop into adults who are safe and effective in society. While George knows that disciplining (being stern with) Lennie will not cause him to develop any further, he hopes that he will be able to prevent Lennie from getting himself into extreme trouble.
Personally, I disagree with this answer. I feel it has many gaps; that it's incomplete. Seriously, I'm answering questions on 'Of Mice and Men' and this didn't help me one bit. Now, there may be other people out there that found this answer quite helpful, but in accordance to my syllabus, this little exert submitted by a teacher who has less important credentials than my Mum (despite her having a Masters in Education I still suck at English lmao) renders my quest to find out "Who else displays the same sense of love in the novella" utterly pointless.