landlord proplems (co signing)

yes gail the girlfriend did sign the rental agreement, the rental agreement was month to month. my son and his grilfriend heard us make the verdal agreement that my name was to be on the lease for (6) mos only. the problem is why would the landlord let the rent get over $7000.00 dollars, i think they should have contacted me if i was still on the lease as a co-signer. i would have help my son out. he could have came stayed with me and gave up the place. also i live in the same complex, and i see the landlord all the time, they never mention anything to me at all. now they are saing i'm will have to pay if my son don't pay. and how can they let the rent get that high, they never gave him a three notice the hold time he lived their which is 3 years. i just don't understand.