I agree with u/patttern2. I was in the same situation, using 4 or 5 times a year only at concerts or festivals. It didn't affect my stutter one way or another, but it took the edge off socially which prompted me to talk more and not care about messing up. I've never heard of a psychotherapy seance, but I'd say go for it. Taking MDMA once will have no negative long term effects. However, I'd strongly advise against frequent use. Have you tried CBD? It doesn't help my stutter directly, but helps with anxiety surrounding it all.