Did Pierre Cheat on Natasha?

In the first epilogue, Pierre and Natasha discuss their former quarrels after Pierre returns from Petersburg. Pierre says he loves Natasha and even if they're at odds when they part, he develops a lot of love for her after they've been parted for a while.

This makes Natasha a little queasy, and Pierre says, "No, I never stopped loving you, it's not that..." He doesn't finish the sentence.

Natasha says their quarrels are silly and when Pierre mentions jealousy, she shuts him up, afraid to open a new can of worms.

After a moment of silence, she asks him, "Did you see her?"

Pierre says no.

Does this interaction imply that Pierre cheated on Natasha at one point in their marriage or is my reading incorrect? I've searched Wikipedia, Sparknotes, and Cliffnotes, but to no avail :(

I wondered who on earth "her" was. Pierre isn't exactly the obvious type of philanderer.