I checked out a book from the library a few years back, and it seemed like it wasn't very recently published at the time. I'm guessing it was published sometime between 1980 and 2005. Huge gap, I know. I can't remember the title, author, or any of the characters' names. Here are the details I know:
There are two main characters. A (teenage?) girl and a man.
The setting is somewhere in Britain or Australia, because I distinctly remember the girl referring to her mom as "mum".
The girl is bored with her life and feels that there is something more out there, or whatever
The man is some guy from the future and outer space who got stuck in the girl's time (the present). And he ends up taking shelter in the woods behind the girls house.
The guy is a wizard or something too, I think. I know that there was a lot of magic involved in this book as well.
Of course they meet, and through a series of events, the reader later finds out that the characters knew each other in an alternate universe or future or past life or something. The girl used to live and work on a futuristic space ship or space colony or something.
The plot was really complicated and weird, so this might not be a good recall of the actual plot. But if you have any clue of what I'm talking about, please help!