I am totally against the concept of Live-In Relationships. The sancity of marriage is lost and the whole thing has no means if Live-In relationship is motivated.
What makes our country stand apart from others is the bonds we have with our family and this would be completely lost if we go for Live-In. Marriage is ideally a commitment not to be marred with age. The word commitment weakens in the case of Live-ins as there is nothing to tighten the bonds. It is just like two people sharing an accomodation instead of going in for a hostel or mansion.
Leave out the person only if you are 100% sure the commitment of marriage will not work out but never live in with someone to whom there is no bond of commitment.