Looking for this one, I think it may be part of a series, (Not sure)

It's about a girl that lives next door to her best friend and I think his mother is never around and he always comes over to her house and there is this tree outside her bedroom window that they always go out on at night to talk. That is about all I can remember it was so long ago that I read the book. For some reason I remember a fast car that he let her drive or something too