He'd end up as one of those people who believes everything on the Internet.

Are they played by the same actor?

Shhhhh, You'll start a fan war.
And yes Arthur Weasley had an affair with a muggle. His only son, Rory, married a stripper-gram girl named Amy (Amelia) Pond. After having a child that inexplicably disappeared, both Rory and Amy also disappeared. Arthur was left with the impression that it was Death Eaters that were responsible.

If it weren't for how much Arthur and Molly were in love with each other and how loyal and dedicated they were, I'd buy it.

Now, figure out how it might have been from a first marriage or a young romance and I'm on board.

(Never mind that Rory's dad seemed perfectly capable with Muggle artifacts.)