How do I recover my money from a debtor whose brother I'm engaged to?

From a female CFB reader

My fiance's brother is owing me N370,000. I borrowed him the money since November last year and up till now he hasn't paid me back and has stopped picking my calls. If he wasn't related to my man, I would called the police because this is tantamount to fraud, but I don't want to do something that would make my fiance call off our engagement. He knows his brother is owing me but told me to give him some time, but I don't think that man wants to give me back that money o. He's no longer responding to my pleas to return my money. How do I get it back without jeopardizing my relationship?