I booked a nonrefundable one-way flight from NYC to Dallas for me and my partner. I am no longer able to make it, but he is still going. Ideally I'd like to get a credit for my unused portion, but I'm not sure if I can make any changes to the reservation without it affecting his flight, since we were booked on the same ticket/reservation. Is there any way to do this?

Also, if I don't show up to the flight, does this affect his ticket? He'd still be able to board, right?

I actually recieved an email that there was a schedule change on the flight departure after we booked it (it's now departing 10 minutes later), so I'm hoping I can maybe use that as some leverage.