I am guessing you missed the part that:
1. To get the XP bonus you have to group with the person.
2. To get the XP bonus you have to be in the same area as the person
3. You are marrying the person.
Not sure you want just a random dude to marry permanently.
Why did they have to make it a marriage. I didn't read that part when I pre-ordered for my son and I. Let that sink in. Sure it's a game, but it's still kind of creepy.