Just my 2 cents:

The original agreement was that you owed zazarb in bitcoin value and nowhere does it say that fiat was going to be involved, or the fact that repayment amount can be reduced due to the fact that fiat repayment amounts will be used if bitcoin goes up too much.

Goose20 fails repayments on time many many times, whilst I think that it's trustworthy behaviour that he had the audacity to respond to this scam accusation and not run away, you're still at fault here at least in my opinion. Especially if all this was as a result of a late repayment to begin with on your part.

If zazarb just held his bitcoin, he would have made a lot more than what he's gotten for you atm. So right now, he is definitely taking a loss.

Consider this - if you take out a loan from a lender, and you're required by the lender to repay more than you originally agreed with because bitcoin went down, even though it says clearly in the contract that you would pay x amount of bitcoins, would you be happy?