not all of this is canon, I made up the reason why you left your town!! (I haven’t completed the game yet either)
Life was good. You had a loving family and a bunch of awesome friends. But that all changed one fateful day.. You see, your younger sibling didn’t understand the concept of fire, and when they see a match and box, they automatically swipe the two together. Obviously they got scared, and dropped the match, causing a fire to start. It got bigger and bigger, as everyone who was smart enough to know how to use a fire extinguisher had already got burnt and died.
Time skip to a month later, and the town is still in ruins, so you decide to leave for good. You decide to start a life at Stardew Valley as a farmer, as that would be profitable in the long run.
You get off the bus, and stretch your legs after the 20 hour bus ride. A young looking girl-probably in her mid-twenties-comes up to you, and greets you
“Hi, I’m Haley! You must be new here, what’s your name?”