The short answer is yes you can sue him, but I do not know how much he has borrowed, so it might not be worth the investment it would take to win the money back via a lawsuit. The first thing you need to do is never lend this guy any more money. His dad is not obligated to pay you back, so there is no sure way you are going to collect. I would also suggest, you find out if there is a small claims court, or something similar in your state, as it sounds to me, from the facts above, that we are talking about a small amount of money.
This answer is a free service to you, and the general public based on limited facts specific only to your issue, and may not apply in every situation. To assure that your situation does not differ from the answer provided above, you should immediately consult a licensed attorney in your state with all the relevant facts and details regarding your specific concerns. Please note, this forum is not a place to communicate all the details, as this forum is public and it could limit your rights in the future. This is not an opinion under the Government Regulations contained in IRS Circular 230, which regulate written opinions about Federal tax matters. This is not such a written opinion, it is an other written communication, and was not written to be relied upon, by itself, to avoid any tax penalties. In order to receive assurances of protection from tax penalties from a written communication, you should get an opinion letter. If you would like to discuss an opinion letter relating to any matter, please contact me and I will explain what is involved and what it will cost.
I am not licensed in NH, but hope you'll find this information useful.
I agree with my colleague, and want to emphasize the recovery part of the equation. There is no point in suing someone if you cannot collect. Even if a judge awards you damages of $5000 (hypothetically), that does not mean that $5000 will magically appear in your bank account. You still need to take the Court's judgment and "enforce" it. And so unless your friend has money to pay the award you make not want to sue him. Having said that, a judgment can be enforced many years after the fact, so if you think your friend will get money eventually, you may want to sue him and register the judgment. You only have a set amount of time to sue him and so you should decide quickly, depending on when you made the loan and/or last received a payment. Good luck.
Atty: 845-704-7777. This answer is provided for informational purposes only and does not constitute legal advice. You should not take action based upon this information without consulting legal counsel. This answer is not intended to create, and does not create, an attorney-client relationship. PLEASE REMEMBER: All claims and legal matters have statutes of limitations and/or other important time periods that apply to them. This means that you must take action on all claims or legal matters within the required time period(s) or your claims could be barred by the statute of limitations or dismissed. Contact our office or another competent attorney immediately to discuss the particular facts of any claim or legal issue you might have in order to learn what time periods apply to your particular situation.