16 year old asked his step mom to the mother son dance 😞😞😞

The YMCA near us did a father daughter paint and sip. Now they are doing a mother son dance and I only found out because his dad said he bought him a suit. When I asked why he said the mother son dance. I said I didn't know about it and his dad said that he asked his wife to take him because I apparently said I had to work. Which isn't true. I asked him about this dance and he got awkward and I asked why he lied and he said he just didn't want to bring it up with me because he didn't want to hurt my feelings since he would rather go with his step mom. I asked why and he said he just feels more comfortable going with her.

There were some issues we had over a year ago where he lived with his dad full time because of a bad situation that got a CPS investigation open. . We have been to family therapy. I've apologized for not believing the situation. We have rebuilt our relationship and I thought we were back to normal. We are even doing split custody again. I thought we were fine and he doesn't even want me to do the mother son dance with him. I thought we had a rebuilt and are healing 😞. Should I bring this up in family therapy. I feel if I force him to take me instead of his step mom it will just put a rift between us again.