I DON'T GIVE A #$&%$
There are a variety of reasons why you might care about someone who doesn't return that feeling. You may be in a bad romantic relationship, or you might be in the post-breakup stage. You could have a parent or sibling who doesn't seem to care about you. Whoever the person is who's ignoring you or antagonizing you, it may be best to learn how to stop caring about someone who doesn't care about you.
Continuing to care for someone who can't return your feelings sets you up to feel miserable. There's no reason for you to allow someone to have that kind of power over you. No matter how someone is connected to you or what your past is with them, they have no right to continue to bring you down.
It's not your fault to genuinely care about that person. But when you care a lot about someone who does not care about you, or cares too little, they can manipulate you and take advantage of you. If you allow them to do this long enough, you lose a sense of who you are and become the person they want you to be, a person you can't respect, and they don't respect either.
CARE ABOUT YOURSELF...........IT'S OKAY!
You may find yourself SPENDING A LOT OF MENTALT ENERGY ON THIS PERSON / PLACE OR THING; that you wish also cared about you. But there is one person you can count on to care about you, and that's you. While you're adjusting to spending less of your time and focus on another person, use that free time to think about what you want. What would you like someone else to do for you? When you figure out what that is, go ahead and give that to yourself!