Realistically, you have 3 choices:
Accept that you will never get the money back and forget about it. I don't know your financial situation. Maybe this would be difficult or almost impossible for you to do.
Badger your friend to pay the money back. Maybe he will and maybe he won't. Either way, the friendship is probably ruined.
Take your friend to court. As this appears to be a verbal agreement, it may be difficult to enforce. In principle, a verbal contract is just as binding as a written contract. But the problem with verbal contracts is that it's difficult to establish exactly what was agreed to, or even to prove that there was an agreement at all. Often the terms of the agreement are vague. Did you ever even say when he was expected to pay you back, whether he was supposed to make regular payments or pay in a lump sum, whether there would be interest and if so how much, etc? Your friendship would surely be ruined forever if you did this. If he doesn't have the money, then even if you win, the court can't force him to give you money he doesn't have. You could be chasing him down for years trying to get payment.
It may be that you are just stuck with paying $5000 for a painful lesson in personal finance and interpersonal relations.
May I suggest that in the future, don't loan money to a friend. If you want to help someone out, just give them whatever you can afford and are willing to give, with no expectation that you will ever see this money again. Choose an amount you can afford to lose.
About two years ago my sister asked to borrow $2500 for a business venture. It didn't work out and she lost the money I'd given her as well as the money of her own that she had used.
Fortunately, when I gave her the money, I told her that it was a gift and no need to pay me back. It was an amount that at the time I could afford to give away and just not worry about it. I made my financial plans assuming the money was gone and just not worrying about it.
Recently she said that she's trying to get together the money to pay me back. I told her not to bother. I don't need it. I don't care. If she does manage to pay me back some day, great. But I am not expecting it or planning on it. So whether she pays me back or not does not affect our family relationship.