How should I make him feel to pay my money back?

I gave my boyfriend $4000 last year when he was in need to pay his tuition fee for his college.We used to live in abroad for our study apart from each other. We both had part time jobs but his job was not much paying as mine so I lend him money at that time. Emotionally I told him he can keep that money. But now we are in our own country and I live with my parents and he lives with his. We are going to get married within 2 yrs. But he never talks about the money I lent to him.And I don't feel comfortable to ask him about that. In our culture, the girl's side should give some dowry to boys.He says he doesn't need dowry but for our families its a culture. And about that money I lent to him its between two of us. Nobody of our family member knows about it. For me, in my country it will take about 4 years to earn that money. How should I ask him back that money? I want to support my family for my marriage. He doesn't have any job right now but his family is richer than mine. Help Please any suggestions?