I don't really have a favorite quote, certainly nothing inspirational that I like to go back to every so often. Instead I have this: "Do you suppose yourself anything to her, but that? You have been too long among your uncle's books. Girls love easily, there. That is the point of them. If they loved so in life, the books would not have to be written." It's from Fingersmith by Sarah Waters.
I use it to kind of remind myself of my place in other people's lives. I too easily fall into a sense of adoration for friends, expecting some great friendship, imagining bonds that will never break. The quote reminds me to chill out, that I don't know people who are looking for that right now.