What do i tell my 4-year old son? 

Our divorce was finalized while my ex was imprisoned. after he got out our son thought we would still be together. I told him simply that mommy and daddy would not be living together. it seemed like he was looking forward to us being back together. That has been about a year ago. we have been going through visitation hearings for about six of seven months now and last week was my ex's first half day visit unsupervised. He had supervised visitation before. It has been a couple of days and tonight after our son's bedtime story(in which a character was getting married) our 4-year old son started to mention his feelings about his dad and his dad's new wife. He said his dad changed and he didn't want him to change. He said he already married me and got another wife. Then he went on to pray to God that we be back together, I was speechless and almost cried. I don't know how to explain to him that these things have passed and gone without hurting his feelings. And I think his dad showed him a shirt he was wearing with a picture of the new wife and him on it.

How should we handle this the best way possible for our son? 

 Was that shirt to much should I confront my ex about that? I

 need help I don't want our divorce to emotionally ruin our son.