Who had other women? I thought we were talking about Snape.

I can see healthy people finding each other again after decades.
But they still would have had a real life in-between. You don't sit around pining over someone you have no hope of seeing again.
That's not really love and it's not even flattering. It's just creepy.

We also hear love songs with the I-could-never-love-anyone-else theme. And that feeling is real. For the moment. Give it a few months and you're singing a different tune.

Someone who's had a good marriage, and the spouse dies while s/he is still young enough, will probably get married again. The people who don't are usually the people who have known only bad relationships.