Before she got married, Sonia kinda fell for Mr. Right... and Mr. Right kinda fell for her (it makes marrying Grandpa Jerk even more puzzling if you ask me).
Except she was getting married and so was he.
(ah, there it is)
Over the years, they crossed paths a few times, but she was married and so was he. And also she clearly had bigger problems than her love life (re: Grandpa Dudebro).
But apparently Sonia and Mr. Right kept meeting by accident, and they were solidly in love as years went by.