I wasn't sure what to contribute at first, but after bpforever1 mentioned perhaps consulting with an another therapist, that was what I decided to second. Your current therapist seems to have a strong opinion in one direction. Not that she isn't necessarily right, but I still think another perspective could be good. If you really like your current therapist, you could ask her if she reminds you temporarily seeking another perspective. Just a thought.

Anyway, it sounds to me that you shouldn't be too hard on yourself about this. To my perspective, you showed great restraint. However, if you eventually conclude that your marriage is no longer beneficial, I would suggest a trial separation for that reason first. Not primarily for the sake of further pursuing the affair.

I wonder if your affair has been a result of hypomania or not. It is hard to have insight into that, sometimes.