i think i deposited fake check

I met someone online and we have been talking for almost month, and he sent me a check, (he is in England and as he said his friend in here, his friend owed him a money instead of sending to england, he sent it to me) it was 2000 dollar, asked me to get 1000 of it and send me back rest of it to england,

I am really unsure about the check and I deposited it, what I have to do? If it is a fake check?
Do i need to go the bank and report my situation?
Please help me? because I am so afraid it might a fake check.