When she divorced Grandpa Loser, Mr. Right's wife started having (or already had them ?) mental health issues, the details of which are unknown to me. So he decided he couldn't divorce her (and my grandmother was VERY adamant that you never date someone who's married, no matter how "separated" they are).
That is, until the wife eventually passed away. By that point, both Sonia and Mr. Right were in their 50s.