sticky rent situation that's partially my fault

[yesisaid]

I am moving across the country on May 1st, which also happens to be the day my one-year lease is up. I live with a friend and her boyfriend, we have lived in the apartment for two years and all three of us are on the lease. We each paid separate checks for our share of the first month's rent, last month's rent and deposit. Since then, my landlord has always insisted that we pay with one check instead of three separate ones. My first mistake was giving my friend a check for my share of the rent each month and then her paying the landlord. This has been going on for two years.

My second mistake was paying the rent for April. I did not find out I would have to relocate until April 10th and told my landlord at the time that I would not be renewing my lease, but my other two roommates would. They told me that they would be finding a roommate but as of today (April 22nd) have not done any looking. I told the landlord in writing as soon as I could that I had erroneously paid my last month of rent to her twice and would need one month of it back. She insists that my friend should pay me, because the landlord did not get the money directly from me, she got it from a check from my friend. My friend insists that the landlord should pay me, since she is the one with the actual money and the one who I have a contract with.

Just when I felt like I'd be able to get all of them in a room together to sort this out, my friend went on vacation without telling me and will not be back until a few days before I leave. For all I know, she will never find a roommate and get evicted for not being able to pay the rent, in which my last month of rent would still be owed to me by the landlord. Now I'm stuck in the middle with nothing. How do I get the last month of rent back that I paid for twice?