Hey, I know the feeling.  I am going through the exact same thing with a friend that is practically family to me also.  God promised me Philemon 1:15.  Check it out for an extra bit of encouragement.  As far as praying Mark 18:19 goes,  try saying "As it is written" before you pray it.  It will put a tremendous amount of power into your prayer.  For example, I loose things constantly.  When I do, I just pray for God to as it is written, bring the hidden things of darkness to the light and I usually find it before I even get the prayer out of my mouth.  But you have to have faith that God will do what you're asking because otherwise, it's useless. 
