HELP. i'm being emotionally blackmailed..?

So someone keeps telling me they 'can't live without me'. He has to speak to me every second of the day, and i really don't want to speak to him. I feel like i can't talk to other people, because he always moans at me after. i really dont know what to do, and i feel trapped|: HELP? oh, and plase dont tell me to tell my parents, because they don't understand. and i don't feel like i can trust any of my teachers at school? what can i do, without getting anyone else involved?!please, and thankyou<3