I agree with the others. You should feel free to talk about whatever it is you want to talk about. Difficult feelings are the bread and butter of therapy. This would be a good opportunity for your therapist to model good self regulation skills, instead they seem to be suggesting that the therapy won't be safe if you continue to talk about the issue. It sounds as though the therapist has anger issues and is afraid or uncomfortable about getting angry in a session.

What was the rupture?