Is he using an iPhone or an Android? (If an iPhone, have him check the SMS box.)
If an Android, make sure you don't have a "text blocker" of some sort running - with his number in it.
Last thing to try is having him ready to send you a text when you bring your phone to your carrier's store during normal business hours - if you have a carrier that has stores that really do troubleshooting. (AT&T usually has a Device Support Center close enough for you to get to, Verizon usually has a little repair department, some TMobile stores have knowledgeable people (what this needs is someone in networking to watch the text as it comes to the carrier, and as it leave the carrier to go to you). - unless you once asked the carrier to block texts from that number and you've forgotten.