This isn't really a question which is addressed by Objectivism except in very general terms: consenting adults have the right to make whatever living arrangements are mutually agreeable.
However, the way the question is stated, I hear the implied question: "Is it immoral to live together before getting married?" This last really has the same answer (no, it isn't), but this is a point in which Objectivism is clearly different from a religious morality. Objectivism holds that a person should pursue their rational self interest at all times, and most especially in romantic relationships. If a particular couple is considering getting married, and they want to figure out if they would enjoy living together, Objectivism holds that it would be perfectly moral to do so.
answered Jan 30 '11 at 18:22
Andrew Miner ♦