Merry Christmas everyone!
Here I brought a pic where Betty is carrying a newborn, and judging the baby's looks, you can tell who's the dad.
My Fan idea thing behind the picture.
Betty didn't leave Simon out of blue, she left because she was scared sheetless of whatever the crown made him do. Betty tried to get over her fear and get Simon help.
But the day she gained enough confidence to help Simon, the nukes were dropped and everything got wrecked. Betty survived and hid in the underground shelters with her family (siblings or parents)
After looking for Simon among the surviving people that hid in the shelters and not finding him. Betty gave up any hope.
After a few days, Betty realized she was preggers. Simon and Betty had gotten busy before he left for his trip in Scandinavia. And now a baby was to arrive.
Betty was both sad and happy for these news.
She was happy, because she was going to be mom.
But she was sad because Simon (presumably) didn't live to meet his child.
And the baby would grow up in the underground shelters. To never see what's outside.
The baby was born, and Betty named him Peter.