I'm sorry to hear you are struggling so much. I can relate to much of what you have said (wife being upset, stressing over having relapsed, worried about reaching out to t...).
Was there more to the sh than just sh last time? or does T just take it *very* seriously? I know I have freaked out about telling T's in the past, but generally, once my risk-level was assessed, being trapped was no longer an issue. I guess it goes with what the cutting means to you. for me, it's generally a way to gain internal control when things feel out of control, it's a release on all the pressure.
Maybe you could reach out to T and tell her you are stressing, and the extent of that stressing? Did you guys talk about how her reaction last time made you feel? Could you bring it up this time with her (or bring it up again)? Even if it's just starting the conversation around being anxious to tell her something, and not really knowing how to describe it...

Also, you did not fail. you did really good for a long time, and you hit a bump in the road. right now it's just a bump in the road, not a splat onto the pavement...