Were the other people on the original lease? Or was it just you on the lease? Did you sublet to them? This situation is kind of unclear how you have presented it.
You shouldn't have just bounced out of there with out getting your name off the lease. If you're the only name on the lease - just because you paid for when you were living there doesn't mean you can just leave. Since your name is on the lease you're responsible for paying for the term you signed for...
Before you moved out you should've talked with your landlord to get the lease assigned to the people who were still living there or you should have subleased to the people living there.
Also why did you give the $ to some random chick / guy to give to your landlord... You should've paid the landlord directly...
It seems like you made some dumb moves and got yourself into a really shitty situation.
Bad roommate situations blow... I had one last year because my friend's psycho girlfriend. I ended up talking with my roommate & landlord to get things worked out, my roommate agreed to take on my portion of the lease so I could move out.
I assigned my portion of the lease to my friend, so he took on two leases (expensive!), talked with my landlord to make sure my name was off the lease and that I was free to go. Then I moved away, and got my security deposit back.