I moved in with my roommate in mid January. I was told I did not have to start paying rent until Feb.1st, with Feb.10th being the cutoff for each months rent. I paid my rent accordingly for 8 months. I was never told I had to give 30 days notice to vacate, since I was not on a lease, although my roommate was. In September my girlfriend was transitioning and stayed a majority of her time in my small room which I paid equal amount as my roommate who had the master bed with bath. I also brought all of my appliances and TV, computer etc to fill the apt, so that we were not just sitting on a matress. In September the landlord informed me that her small dog could no longer be in the house. I said that is fine and notified my roommate that I would be leaving in 2 weeks, I considered that fair since they were basically kicking my girlfriend and her pet out, and me too in circumstance. I moved out on Oct 2nd and told my roommate that I would pay him for the 2 days in October. His response was, I must pay him for the whole month of October even though I won't be living there anymore. Is this fair? He has been calling and threatnign me if I don't pay. SHould I pay?

Yes. If you are a month-to-month tenant then you are required to give 30 days notice when moving out. If you were a week-to-week tenant then you would only have to give notice of one week. The basic rule is that you give notice that is equal to the frequency with which you pay rent.

Well I would have to say it depends on what the landlord said to you. If the landlord said something like the dog can't stay here anymore, then the decision to move was yours and you were required to give notice equal to one rental period in the absence of a lease specifying something else.

However, if the landlord told you that you need to vacate the premises ASAP then the decision to move was not yours, but the landlord's.