What happened to Rosemary is bad enough, but when you find out that she was The Giver's daughter, and that he watched her "being released," and that HE plans on "being released" himself now that he's finished teaching Jonas, it takes on a whole new level of depressing.
The fact that the Giver didn't actually finish watching the release, but had to look away. While a perfectly sensible thing to do, the matter-of-fact way it's stated adds to the poignancy of the scene.
Rosemary HUGGING the Giver and giving him a kiss on the cheek before going to the Chief Elder to request Release. To think that he (with good reason, but still!) caused her pain to the point that she felt the only solution was to TAKE HER OWN LIFE and yet she loved him still (and presumably was feeling a bit guilty about what she was about to do to him)... sorry, it's getting really hard to see all of a sudden.
The fact that Jonas's parents—and everyone else but the Giver (and later Jonas) in the book—are ignorant to the idea of love. It's so difficult to fathom— parents who don't actually love their children is a hard concept to swallow. The delivery of it was so simple too; not dramatic and heart-wrenching which made it even harder to read.
Made even MORE heartbreaking by the fact that Jonas quickly realizes that his friendships with Fiona and Asher are doomed- because, while he loves THEM, they are literally incapable of reciprocating that love. It's at that moment that he first starts to grasp just how empty and lonely his life is going to be.
Jonas enjoys his role as the Receiver at first, receiving all kinds of happy memories such as riding a bobsled, genuinely happy families, holidays, and various world cultures—all things that happened before the rise of the Community. Then comes the memories of animal poaching and war, as the Giver's way of warning him that pre-Community life wasn't all sunshine and rainbows.
Jonas's breakdown when he finds out what Release actually is- and realizes that he just watched his own father (whom he had always thought of as caring and gentle, especially around newchildren) commit infanticide. The poor kid actually ends up rocking back and forth whilst curled up in the fetal position!
Turns into a bit of a Heartwarming Moment when the Giver comforts him and even invites him to spend the night.
The ending lines.
"For the first time, he heard something that he knew to be music. He heard people singing. Behind him, across vast distances of space and time, from the place he had left, he thought he heard music too. But perhaps it was only an echo."