You signed an agreement with the landlord and while your names are listed on the lease as two people, you are each jointly and severally liable for the monies. This simply means you are responsible for the whole amount as is he. If you want to clear it up, you pay the whole amount and then sue him for his half. As to the 60 days notice, you do need to give it in writing, otherwise your lease may be automatically renewed. This means you would held liable for the rent up until the time the landlord was able to relet the premises since the landlord had to mitigate his damages. As to your security deposit, that could be used to offset the amount of rent owed but your landlord is required to give you a list of costs, repairs and the receripts for those repairs. This is usually supposed to be given to you within a certain amount of time and if he didn't do so, he may be actually liable to you.