I'm going to preface this with I'm in exam mode so sorry if I don't make much sense (not much sleep!)
A ONS is a huge deal (obviously) and if she was not going to cover it then you need a new MC
When I had MC (we only had about 6 sessions... if that) he didn't want to focus on the infidelity. That said there were safety issues in our relationship as well. Your MC is there for you and your wh not you there for for MC
I know you feel things are going well, and I truly hope you continue to feel that way. however don't be too harsh on yourself if that changes.
Also, it must be truly difficult with your parent's with you, I hope you are both able to put some time aside each night to discuss things though.
Don't stress about MC, assert your needs if it doesn't get covered