Pretty simple achievement.
If you're bad, save the game, give all your money to Avo and become Attractive. If you're evil (and ugly), then you're going to have a hard time.
Notes from the comment section: She'll have a yellow heart over her head when she's ready, all you need is a ring in your inventory and to talk to her and the option to marry her should come up.
Meet a girl, be attractive, flirt with her, propose to her. (The wedding ring can be found at almost every Item Store.) Buy yourself a house (The cheapest is in Bowerstone South) and have her follow you to it. Make sure that you're living inside it at the time, and the option to marry should appear. Get married.
Once married, have your spouse follow you around until your find somebody else who has a Love Heart above your head. Should be easy if you're attractive and pure at heart.
Once you find somebody else who loves you, just flirt with them. And the achievement should pop. If you want to take the right route, go off questing (make sure your house is upgraded fully) and return eventually to your wife. She should have a Gift waiting. If she doesn't then you need to butter her up by giving her gifts first.
I personally got this after marrying Lady Grey.