I absolutely believe that a lot of the people in our lives are there for a reason. Not everyone, but I think the people we are closest to are those that we have shared multiple lifetimes with, and we continue working out whatever spiritual lessons we need to learn with/from them, until we finally get it sorted out. I have had many instances in my life where I have met someone and either felt instantly at ease with them, or have instantly hated them...without knowing why, as I knew nothing about them...at least not that I remember! So I think reincarnation is the best explanation for that - which also explains why we keep meeting up with the same people, lifetime after lifetime.