Now is the winter of our discontent/ Made glorious summer by this son of York,
– Opening lines to Richard III, writ by William Shakespeare.
A millennium ago, the sage of six paths, together with his brother, connected people together with chakra. With that they brought forth an eternal peace after the eternal wars that had been waged across the lands, thus ending the cycle of hatred.
A century ago, Senju Hashirama, together with Uchiha Madera, connected the clans together into villages. With that they brought forth an eternal peace after the eternal wars that had been waged across the lands, thus ending the cycle of hatred.
A decade ago, Uzumaki Naruto, together with Uchiha Sasuke, connected the villages together after the fourth great shinobi war. With that they brought forth an eternal peace after the eternal wars that had been waged across the lands, thus ending the cycle of hatred.
Shikimaru knows that this eternal peace shall go the same way as the previous ones. That is why
A year ago, he proposed to Temari. She said yes.
A month ago, she announced to him that she was pregnant with his son.
A week ago, she left on a C-rank escort mission.
A day ago, she wrote back to tell him that there hadn't been any complications, and that she'd be home soon.
A second ago, Temari announced that she was home.
Now Shikamaru goes up to her and hugs her. He knows that this eternal peace is nothing but a temporary ceasefire, that the cycle of hatred shall never end. Because of this, he lives. The ceasefire shall end, so he chooses to make the best of it while he can.