Need help and advice on how to pay back $20,000++ default on BTO downpayment?

I have been with my boyfriend/fiance for 5 years. We have a BTO and have already paid the option fee of $2000 and the initial $18,201 5% downpayment after signing the agreement for lease. Supposed to be collecting our keys in one year, but due to circumstances, we are calling off the marriage. Now we have to pay back a big sum of $20,000 ++ altogether including some money spent on wedding preparation when we are both not earning much. If any similar experiences and resolving methods please share...