Poor Robin (who is sometimes called Robert) sure gets the short end of the stick, huh? He falls in love with Moll early on in the book, when she's still in the first blossoming stages of the beauty that she takes such care to emphasize. He seems like a good guy, and we'll soon learn that falling for Moll usually never ends well for the guy, so our Robin is probably headed for some heartbreak.
It's not really his fault that she's actually in love with his brother and has no patience for Robin. And the more interested Robin gets in Moll, the more repulsed she is, and the less interested she is in being with him. A naïve Robin assumes she's too noble to sleep with him when really she has been having sex with his brother nearly the entire time he's known her. She stays away from him because she doesn't want to be "a whore to one brother and a wife to the other" (104). And even when Robin eventually gets his way and marries Moll, he's just not the man she wants. Their relationship lasts for a few years, but it's clear it's not a love match.
He's one of the few characters to whom Moll gives a proper name, but it's probably not his real name, and the pseudonym she chooses isn't even that flattering. (Check out "Tools of Characterization: Names" for more on this.) When he dies after a few years of marriage, it's basically a relief for everybody involved – except him, of course. His kids are sent to live with his parents and Moll parts forever with the family she'd gotten to know just a little too well, if you know what we mean.