How to Get Married in Fable II
The Spouse Achievement
Getting married in Fable II is actually fairly easy — at least compared to the real world. Before you try and pick up a new husband or wife, be sure to get two things: a ring and a home. Rings can be purchased from a jewler or found/stolen just about anywhere. Houses can be purchased by targeting the deed outside of any building and choosing to buy it.
Then, find yourself a potential spouse. Perform favourable expressions (flirting, funny or positive social expressions) to get them to like you, and then give them a ring as a gift to propose. They may be so forward as to ask for one, or you may have to pop the question all on your own.
To see how much someone likes you, and how close they are to accepting an engagement ring, simply press the left trigger (LT) while targeting them, and take a look at the bar. If the person is a potential spouse, a ring will appear on the bar, indicating how much they need to like you before accepting an engagement.
Keep in mind, choosing a wealthy mate means you'll need a nicer ring to impress him or her. They may also be less satisfied if you move them into sub-standard housing. Also, some characters in the game are bisexual, meaning there are characters of both sexes eligible to become your spouse, whether you choose to play as a male or female Hero.
Once you are engaged, your potential spouse will automatically follow you. Lead them to the house you've purchased (or buy one now if you hadn't done so) and take a look at the deed. You'll have a new option, called "Set Marital Home". Once you do so, your marriage is complete. You'll unlock the marriage achievement, The Spouse, and your spouse will move in.
The Spouse
Marry a villager, or attend the wedding of another Hero.
10 
You'll then have the opportunity to earn another achievement (The Parent) by choosing 'Unprotected Sex' when you, uh, consummate your marriage. You can wed again the same way after this marriage, or while it's still going to earn another achievement: The Bigamist.