When the weather is fine

"I know that sometime, when the weather is fine, I will be with you"
That was the last thing Harry said to me before he turned around and jumped on the bus and jumped out of my life.
That was three years ago, when I was 15 and he was 16. At that stage we were best friends, we were super close and I was in love.
Fast-forward three years and Harry appears back in my life. But he isn't the Harry I once knew. Gone is the boy who would walk into my room with a nerf gun to wake me up in the morning, gone is the boy who would take walks with me at 2am on a Saturday to get a mcflurry and go to the park. Gone is the free, fun loving, bright Harry. Hello to the dark and brooding, tall and muscular Harry who I think has a tattoo. At least that's what I've heard.
But what's he doing back? And why did he leave in the first place?