Breakups

Do you know why do people dump other people or why do they get dumped? Let's think about it. There's a boy and there's a girl (well sometimes two girls/boys or nowadays even three) and they like the other and they want to live their lives together forever and things like that. Then the boy or the girl begins to change, he/she doesn't really like the other anymore. And why's that? I think that's because everyone likes the unknown and doesn't like the already known so much and everyone wants to get more adventure in everyone's Life . Of course this can be rubbish but I think it goes like this.