I had an idea that was inspired by the Fallout 4 game. The people go into a vault and are put into suspended animation for years. One of the people is awoken and greeted by a young attractive person. They are also told by the person in charge that they aren't able awaken everyone at once and that the main person's famity will be woken up later. Maybe their spouse died before they went to the vault or they were told the spouse died years ago. So the main character gets closer to the person they met earlier. The pain of loss of their spouse is lessened by this person and they eventually begin a sexual relationship with the person. One of them eventually gets pregnant. Either when it's close for the baby to be born or after the birth the main character finds out that the young lover was actually their child who was only a baby when they entered the vualt.