I think the fear of closeness and the fear of getting into this new difficult subject are probably related. Sharing really tough things with someone who cares about you and knows you well is going to another level of intimacy in a way. So I could understand where that anxiety and fear would come forward at the prospect of that even greater connection.

There is nothing that says you have to talk about the difficult stuff next session, so you could reassure this scared part of you by deciding not to talk about it quite yet-- wait another session or two maybe. Instead you could talk to your T (as it sounds like you're planning to) about all the feelings that have come up just at the idea of that discussion.