Love is unconditional. Love is acceptance. We can not always be what others desire of us and others can not always be what we desire of them. If we choose to love, we must also accept that we may be hurt, we may not be loved back, unconditional and acceptance.
We don't. Why would you say that? When someone had a crush on me, I was always nice to them. I found it flattering. A lot of them are still my friend. If you are a mean, hateful person, I suppose you would hurt them, if you aren't you can handle it in a way that is sweet and gentle.
We like to test their perseverance in dealing with our good and bad sides. It isn't that we don't love them any less, it's just that we want to be sure they will stick around.