The problem with trying to keep a relationship going with hardline JW's who have made a vow of loyalty to Brooklyn diktats Jehovah (women seem particularly susceptible to this - runs for cover) is that the elephant in the room is so huge that there is no room for the people. Like Diana said "There were three of us in the marriage and it was a bit crowded."
Also, the problem in the relationship isn't actually the person who has left or the person who is still a JW, it's the blooming organisation that dictates every facet of their life. The people are fine, it's the rules of the organisation that ruins things. But it's not like you're allowed to point that out or anything, because one of their rules is never to speak to or listen to you.