Yes, you will have to show it was a loan intended from the outset to be repaid.
You could sue him in the small claims court. He will say it was a gift; it was to pay back money he lent you; it was to pay for something you benefited from (holiday, housing, anything); he paid it back...
The court would want to know why you are pursuing it after three years when he hasn't made a single payment.
Even if the court find in your favour you will probably have trouble enforcing it.
You can't engage a debt collecting agency until you have a court judgement - they don't go chasing debt just on your word, they will want proof of a debt.