There are only three events that Leonard would say changed his life.
The first—he was wanderin' through the old family library. His folks still kept books, though they were rotten with mildew and the glue on the binding long gone. Artifacts like that don't last long in the Georgia humidity, temperature controls be damned. There was a giant book about anatomy. The pictures were fading, the pages stank of somethin' awful. But it was the best book Leonard ever laid eyes on, second only to the Bible. Cracking open the stiff pages isn't when he decided to become a doctor, that was later. But the seed was planted here.
The second—he met Jillian. Also at second, when he married Jillian, and when that marriage fell apart and Jillian divorced him. The point is, Jillian is number two in his life. She always has been, and maybe that's the reason why their marriage broke in half. He doesn't want to think about it. It's still too soon and still too close to his heart. Leonard doesn't remember much of the good or bad right now, to be honest. It's all feelings that average out at bittersweet. At any given moment, they range anywhere from anger to grief to nostalgia to apathy. But Leonard's been in relationships before, he's taken his psychology classes, and knows that time heals all wounds. This one's a doozy, he's sure of that, but it'll pass. Besides, there's a boy—James—who's makin' a very strong bid to take Jill's place.
The third—Joanna. The day he became a father. The day he wasn't the racing against the cesium seconds in an emergency case, givin' the hollerin' newborn (or taking a limp body) to a proud and tired (tired and sobbing) mother, but to his wife. The day when he was the one, not some lucky Joe, who held life in his arms. Joanna, meaning 'God is gracious.' And Leonard believes it, seeing this life that he created move her tiny fist to touch his finger. She looks up at him in perfect trust and that day he swore he'd be a better husband and the best father. That day he made another vow, one of many, that he wasn't able to keep.
Leonard McCoy is human. Born and raised in Atlanta, Georgia, of the United States. His family's got a long history of men who served their country and their planet. They pride themselves on being able to trace that lineage back to the War of 1812, when Leslie David McCoy served under then General Andrew Jackson in the Louisiana campaign. There's some object signed "Old Hickory" stuck in the family albums. Several members of the McCoy clan participated in the Spanish American War, Civil War, the Great War, World War II, Korea, Vietnam. They're listed for Yugoslavia, Eugenics Wars, World War III, and the Earth-Romulan War. Leonard wasn't expected to enlist in Starfleet. The family has at least four McCoys, Leonard's cousins of various degrees and removals, already in the ranks.
But he has always enjoyed irony, and finds his current situation to be extremely ironic. He's never thought of himself as a soldier and he's always hated war. Starfleet claims to be a totally peaceful operation devoted to science. To be fair, they are at the cutting edge of research in practically all fields. But Leonard knows that science and war go hand in hand. The biggest leaps in technology come from weapons development, revolutionary medical techniques are discovered from bodies shredded on the battlefield. Things are generally discovered much faster when your advantage, and therefore your life, depends on how you can harness the atom, or how fast you can jump to warp, or how precisely you can phase matter.
Leonard is human, and he feels like hell. This boy James, who randomly insists not only on monopolizing his free time but also calling him 'Bones,' is real annoying. Like you wouldn't believe. He's also real immature. Jim's already in his twenties. By that time, Leonard's pretty sure that kids've got most of their kinks out and no longer feel compelled to get into bar fights against four Starfleet security guys. Jim still feels that way, and you can see it in the way he carries himself (also in the beautiful black eye and busted nose he's sporting). The guy's got a chip on his shoulder and somethin' to prove. Leonard's not sure why Jim chose to stick around him, but he has.
Another time, another place, he's not sure he'd give the boy the time of day. He's a busy man. But misery loves company, and Leonard feels miserable. Divorce, a lost family, broken promises—he's got nothin' but his bones left. Jim's a pain the ass and a first class idiot (he doesn't care what they say about the kid's aptitude charts. Leonard's always called 'em like he sees 'em), but the kid needs him. Maybe he's doing this as an apology to his girls. God knows it's too little too late, and they won't ever know about it. But it's still an apology, a firm resolution to himself and God that he'll try harder this time.
Atlanta aint the country, not by a long shot. It's a booming city and Leonard's not a country boy. It's in the South, which is another thing entirely. Jim likes to poke fun at his accent (Leonard thinks that's rich—a Midwestern farm boy straight from the cornfields of Iowa, who knows how to drive a damn tractor, making fun of his Southern accent), and grimaces at the music Leonard likes. He gets defensive on both counts. He aint changin' his accent for no one, though it's been going away on its own accord. And in his opinion, country music's the only thing worth listenin' to at all. It's simple and true. It makes him laugh, it sobers him up. What else could a man want?
Sometimes, just for kicks (because he can't believe some of the scrapes Jim gets himself into), Leonard compares himself to Rick in Casablanca. Jim's Louis, that annoying Frenchman who somehow manages to stick his nose into everyone's business. The parallels stop there, but it cracks him up to think about it when he's watching Jim try to explain to Pike why he felt the need to fly a ground shuttle at Mach 3. Leonard, like they rehearsed, saves Jim's ass yet again by providing some ridiculous excuse (Pike's not fooled) and Jim gets off the hook without getting tangled in academic suspension. As they leave Pike's office and go for lunch, Jim says one of the freakiest things he's ever heard.
"Bones, I think this's the beginning of a beautiful friendship."