I'm thinking (hoping!) this is a joking response to a question I saw the other day about how many wives it's okay to have. In which case I would say as many as possible, as long as they continue to buy me pretty things ;)
But in all seriousness, I think the bond between husband and wife, or even between boyfriend and girlfriend (or a homosexual couple - you just need to swap the nouns around a little bit), is something that is incredibly special and should not be cheapened by attempting to carry on a relationship with more than one person. Plus think of all the nagging you'd get from having more than one wife/girlfriend. And all the dirty socks that would be left on the floor if you had more than one husband!