kudos on being the parent you are. sorry you are having probs with the ex tho. sounds like she is not the "mature adult" to talk to in a constructive manner re you son due to her inability to keep the topic on son. that's not your fault it seems but hers. wanting to have a "mature conversation with someone" who may not be mature is just gonna frustrate you. i assume she has her own time with y'alls son. like he goes to visit her etc. so she's engaged in his life. perhaps stepping back a little with all the conversations would help. if she approaches you about something you can answer her question but keep it simple or suggest she ask your son. he's old enough to communicate adequately with her.

it would seem that having a constructive conversation with her is not going to be as fruitful i'd you'd like. so perhaps some "healthy distance" from her is the answer. idk, but thought i'd throw that out to you. having expectations of others that are not capable of fulfilling them is futile. can't change them either. been there, done that. you're doing all the good things for your son. i'd say keep your focus on him and use all that positive energy you have for your relationship with your son.