I'm thinking of leaving 3 months early from an apartment that was rented to me as a favor and I didn't have to sign a lease but more so on a good word
Why do you want to leave the apartment early?
I'm afraid the cheap landlord will have me evicted if I have problems with neighbors or his drug deals go south
You should keep the apartment if you made a promise. If there are illegal or drug problems in the neighborhood, you may want to leave early.
It also that I'm just trying to be a dick and make the landlord lose money.
It does depend what you want to accomplish. Breaking your word could get you in trouble if you want to rent from somebody else.