Dear CAB readers: How do I collect my money back from my ex?

From a female CAB reader

My ex and I dated for three years and were actually planning to wed. We got engaged April last year but because of family issues the wedding was called off in November 2012. Despite the end of our engagement, we kept seeing each other on and off for several months until we finally broke up in August. I was hoping we would get past our problems and go ahead with the wedding but that didn't happen. Now, here's my problem. I gave my ex N720 thousand naira last year for a project he was involved in. I borrowed him the money because I thought he would be my husband and if the business venture succeeded it would benefit both of us but since we have broken up and he's now seeing someone else I want my money back. I have been asking him for the past two months and he's telling me rubbish and has stopped picking my calls. The business is doing fairly well and he's making some money from it; is another woman supposed to enjoy the fruit of my labour? I want my money back. How do I go about getting it back?