Originally Posted by
Buffalobiian
@rockmanj: it depends on how that whole situation came about. Did he move out, forgot to cancel his account, and you guys have been getting free gas in the meantime? If so, I think its only fair that you paid it. Sure, legally it's his fault and you don't owe him a dime, but looking at it from a moral perspective whoever used it should pay it.
I'll assume that the former agreement was that the bill went under his name, but you paid half while you two were still living together? There's a shared understanding that even though he's legally liable for the costs, in actuality you both have agreed to pay for what you used (and assumed a 50/50 split for simplicity's sake). This is just an extension of that since he forgot to terminante your agreement.
I don't think you should be pressured into a lump sum payment though. Try to make repaying him back as high a priority as possible without starving yourself or something.