Based on your post--I think "leaving this ugliness unresolved" would be very, well, ugly, and unresolved. If it were me, at least, this would eat at me. It may be very difficult to tell her everything you've discovered, and yes, to admit guilt... but maybe it would feel good in a way, to be honest about it, and get it off your back.

So, I guess I would say: go back (or to another T) and be honest (even if only eventually). Because at some point you will need to deal with whatever drove you to researching her so much. Good luck.