Short answers, pulled from the story.
Patroclus was a young boy from the town of Opus who accidentally killed his playmate Clysonymus during a game of dice. This tragic event forced him to flee his home forever and live under the protection of King Peleus in Phthia.
Patroclus died when Apollo removed his wits in the heat of combat, allowing Euphorbos to strike him with a spear first. The Trojan prince Hector then stabbed Patroclus in the stomach while the battlefield raged around them.
The ashes of both heroes were later buried together in a golden urn near the Hellespont. This final act honored the bond between two friends who had shared everything but life itself.
Later Greek authors argued fiercely about whether Patroclus and Achilles shared a romantic relationship or only friendship. Aeschylus called Achilles the erastes while Phaedrus labeled him the eromenos in their dynamic.
William Shakespeare placed Patroclus in Troilus and Cressida as a character whose presence made Achilles lazy. In this play other characters complained that the two spent too much time having sex instead of fighting.