You care, they don't. Then leave them be. Maybe they're cold, maybe you're overly attached to something you shouldn't be. Either way, it's not yours, you can't have it so just forget about it. Focus on yourself. Really isn't rocket science, just needs said clearly.
Apathy is a defense mechanism: it is there to protect you. Carry your love with you in your journey through apathy, to love is to wish well for another even when we no longer can influence or be involved with the person who pushed us away, to love is to save yourself.