Is this a companion fare (buy 1 get 1 cert)? If so no you must be on the exact same flights.

If this is not the companion fare. Then what you do should not have effect on your partner. If this is a RT your return will also be cancelled. it may be best just to call and cancel yourself from the reservation. There is a cancel option that bypasses the "My wallet" where you do not have to pay the fee at time of cancel, only at rebooking.