I personally don't have any problem with a loan and to take chances that front-loading the investment might pay off better than buying incrementally. Each of us is free to exercise those kinds of potentially reasonable gambles - even with long term investment money.
Everyone has no problem with borrowing, it's free to do for certain interests, especially the use of the money taken is placed in investing in bitcoin.
I think that the area in which OP went wrong was that it appears that he was calculating that the BTC price will go up during the next two years, and he seems to calculate that into his plan as if it were guaranteed, and even if the odds might be greater than 50% that the BTC price will go up in the next two years, that seems to be allowing for too many loose ends in regards to how to play a 8% to 10% per year interest rate that guarantees a certain level that he has to cover in the loan just to pay the servicing of it and how much the loan is costing him.
Predictions like this are normal things to happen in my opinion, because the OP could have tried to calculate bitcoin's journey when it reached the previous ATH, so that in the next two years bitcoin can provide a large return on the investment it makes. The time accumulation the OP was trying to calculate seemed to follow a four year cycle, so he decided to invest and take the risk of borrowing money from a bank.
However, the problem that will be faced in the following month is how to pay the bank's monthly fees, especially if you do not have other sources of funding, such as cash flow and/or money from other proceeds. Honestly, I would like to know how much the monthly fee must be paid to the bank by the OP?
He also seems to NOT have other funding sources, such as a cashflow and/or other monies to assure that he does not have to sell his bitcoin..
The biggest problem arose here, there was no other source of reserve funds as he started to run out of money to cover the bank's monthly fees, so when faced with difficult conditions he would decide to sell bitcoins. Thus the investment he made did not get any profit and you could say he failed miserably in implementing this investment pattern.