Your landlord can evict you and sue for back rent.
If your friends landlord lowered the rent for him/her and then after moving in with him/her, he/she decides to move out, then the landlord will most likely raise the rent again.
Sure.
Generally he can go back as far as you owe the rent. But a landlord can only evict you for not paying the rent, not for money that you owe for back rent. If your landlord accepts your money for the correct amount of rent, he cannot evict you for the back amount, but he can sue you for that.
No.
The tenant owes the rent to the landlord up the day of a foreclosure sale.
Yes the landlord can be sued for breaking the lease.
When a tenant files for bankruptcy, this will apply to any money tenant owes. In the case of rents, which is not a form of credit, you still must pay to landlord your rent or face the probability of eviction. If you owe your landlord back rent and declare bankruptcy, then you can include this back rent as part of your debt. Back rent is considered a form of credit, because you owe this money to your landlord and he has continued to grant you the right to stay there. It should be noted that whenever a landlord commences eviction proceedings against a tenant, it is never on the grounds of owing back rent. Your landlord's claims against you in small claims court covers that issue.
A landlord cannot legally harass you for rent if your rent is not in arrears.
If there was a lease, the landlord has an obligation to try to rent the unit after the tenant leaves. If he is unsuccessful, the tenant owes for each month that the unit is vacant, through the end of the lease.
If you were evicted for non-payment of rent, your landlord COULD file a lien against you for the unpaid amount.
I have to pay rent to my Landlord
Your answer depends on what you want to do.If the rent is paid for the full term of the lease agreement, then the landlord cannot rent the unit until the rent runs out.The landlord may want access to the unit to confirm that everything in the unit remains undamaged.If the landlord wants to rent the unit just because it's vacant, the landlord should refund the 'unused' rent to the departed tenant.