In Ally Condie's young adult novel Matched, protagonist Cassia finds herself in a conflicting love triangle. She has been matched to marry her best friend Xander Carrow, but circumstances also bring her closer with Ky Markham, someone she has known since her childhood. She knows she could develop romantic feelings for Xander, but the more she gets to know Ky, the more she falls in love with him. Since her emotions center around her friendships with Ky and Xander, her growing relationships with them help develop themes concerning love and friendship.
One passage concerning friendship can be found the moment she starts learning Ky's life story concerning being a child in a war zone. Ky begins sharing his story with her by writing it down on napkins she can read privately. The more she learns about him, the more she cares. We see her caring feelings while, in Chapter 20, walking with both Ky and Xander in the game center, she gives him a deep look, hoping the look will tell him, "[She's] read his story, that [she] cares." She further shows the how much she cares and the depth of her friendship by stating how much she wants to keep Ky safe:
The one thing I can do for Ky is to help keep him safe, to hold onto what I want to say until there is a good place to say it.
Since both of these passages show just how much she cares for Ky and puts his needs first, they are excellent passages that serve to develop the friendship theme.