Broke tensioner pulley when replacing drivebelts! subaru, help!?

Well i've never been extremely knowledgable when working with engines so im having a hard time figuring out what it is i broke. First of all, the car is a POS, i was replacing the drive belts and the one that is connected to the altenater went on good. but the other belt was looser than it should be, bending more than an inch, so i tried tightening the tensioner and the part where the tensioner threads into the smallest wheel busted. what is this piece calls and can i find it without going to a mechanic? I dont really have an arm and a leg to spare. there are 3 wheels that the belt goes on the smallest wheel that is lower is the one that broke, the wheel is fin, just the little metal piece that connects to it so that the tensioner bolt can thread through it busted off. Of course now the belt slips when i start the car because its still loose and produces a squeeling sound for about 5 seconds, and the car clunks when first accelerating from a stopped position. any help would be awesome. its a 2000 subaru legacy AWD L wagon.