I don't love you means that I don't care for you the same way you care for me.

I hate you means there is nothing I like or respect about you.

You can still like someone and not love them. When you hate them, you have no use for them at all. They're irrelevant to your life.

When you don't love them, but don't necessarily hate them is like rejecting someone who has a crush on you. You don't love them as much as they love you, but doesn't mean there's something major that will make me despise you. You're just not my type. LOL