Temper and Temperance

I am losing my temper with Doc quickly.
I have been, for all intensive purposes, living with Cowboy these last couple weeks. While this is not the standard or accepted, much less ideal, Baha'i relationship, this relationship is far healthier than the vast majority of others I've been in, and, frankly, I'll take progress without complaining that it's not perfection.
In any case, Doc is Cowboy's roommate, and a medic, like myself. That, however, may be where the similarities end. Doc constantly borrows money from people- occasionally paying small sums back, but leaving a trail of large debts behind him. He currently owes Cowboy over $700.00 (and has for about a month) but payed me back $40.00 of the $50.00 he owed me a week ago. Since this, he's told Cowboy several times he intended to borrow money from me, though has, so far, followed Cowboy's advice (or warnings, if I know Cowboy) not to do so.
When it's not money, it's Cowboy's motorcycle. Doc will come out and ask for the keys, generally not asking permission and, more often than not, avoiding telling Cowboy where he intends to go on the bike. He complains and whines about not getting his way, and continually complains about anything he's done to help around the house, or even on the bike.
Cowboy knows how I feel about all this, and, frankly, I have no idea how he's letting him even live here right now, but that's between them. Doc is usually smart enough to try to leave me out of it, but has, at some points, brought me into it. Cowboy and I now have a pact that neither of us repeat what's discussed between us to Doc, for any reason.
Doc's fiance lives in Florida, and he has brought another girl to the house to spend the night with him on at least one occasion, though I only found out about that by accident, despite it being while I've been here, so who knows how many times it's happened.
Any respect I might have had for him when I met Cowboy has since dwindled to nothing.
He's worried I'll tell his fiance, and, honestly, I think I should, however, that's not something I want to be a part of, as I know it would certainly end his friendship with Cowboy, and that's going to be over the second Doc proves fully unwilling to pay his debt to Cowboy as I already know he is. Cowboy just keeps hoping for the best, saying he can't pay these bills by himself- but that's exactly what he's doing as it is.