AA has been pretty good to me in terms of consistency with seat selections. Follow some of the suggestions noted earlier and you may have better results. I'm also assuming your partner has a different last name since you didn't refer to a spouse. If you don't make reservations at the same time (same phone call or Web session) you'll get different PNRs (Passenger Record Numbers) and the airline may not know you're flying together. You can call and ask them to link the PNRs so they don't put you on one plane and your partner on another if schedules change.

The only recent trouble I had was booking a DL flight to Scotland through Orbitz. It was one of those flukes where Orbitz was about $200 less per person for the same flights than DL's site showed. My husband was 70 at the time, over 6 feet tall and having back problems. I selected an Aisle/Middle combination on the transatlantics. I checked a few weeks before takeoff and the seat assignments were trashed- apparently they didn't get passed from Orbitz to DL. I called until I found an agent who would get him in the aisle again. Then our flight from MCI-JFK got diverted to CVG and even though we made the flight from JFK-EDI we found out at the Delta Club in CVG that our seats to EDI had been trashed-again. An angel in the Delta Club fixed that. Same story on the return- I called and begged and he got an aisle seat and I got a window seat- in rows across from each other! The other 2 seats on both sides were occupied by people traveling together so we didn't try to move everyone around.

Which is a long-winded way of saying- never assume any seat assignment is permanent- keep an eye on it and call immediately if something goes wrong. If Person A says no, be polite, hang up and call again.