That's a pretty big thing to forget. His reason for it doesn't make much sense, either. I would imagine he hears a lot of painful histories and is trained to be present in session. I don't think it's a minor offense. It's what he's paid to do. I guess I would want to know if he forgets other things you've shared or was this just a one time occurrence (even so, that's not the topic to drift off of and forget).

You could be testing him...but is it worth it? Have you considered taking a break? You can go back, but it will give you some time to sort through things for yourself, maybe see another therapist to discuss this with.