Honesty is the best and should be the only policy but it becomes so difficult to be honest when you allowed yourself to be defeated by temptation. The fact is, God see everything and He knows everything and what ever the consequences will be facing your significant other with the truth, it will never be as bad as living in the lie.  You would have already committed the offense in the face of the Lord, don’t commit yet another wrong with a lie. And remember when you confess and ask forgiveness from that special one you need ask forgiveness of the Lord too