I would look first at the contract, if no contract then where did the transaction take place and how much was the transaction? Use this to determine which state governs the contract.
For a court to render a judgment against a defendant, there has to be personal jurisdiction, subject matter jurisdiction, and proper venue.
Personal Jurisdiction: If the defendant is not a resident of Texas, a Texas court can have personal jurisdiction if the defendant engaged in certain activities in Texas. Was the borrower in Texas when he borrowed the money?
Subject matter Jurisdiction: the amount of money you are owed will affect which court you can sue in. Depending on the court you are suing in, you might have to go to the court in person.
Venue: Generally, proper venue for a lawsuit depends on where the actions that form the basis on the dispute occurred. With limited exceptions, a plaintiff cannot simply sue based on his or her own residence.
If you are suing the person and he is not physically present in Texas, you will still need to serve him with process.
I hope this information answers your question. If you need more information, simply add a comment or call me. Good luck!