You kept things bottled up inside, basically lied to yourself AND your wife AND her girlfriend for TWELVE YEARS. And now you've made this drastic, 180-degree turn in the space of what, a month??
I'm not trying to invalidate your feelings. You've realized what you feel, what you want and what you don't want. Great.
But your apparent desire to change things quickly needs desperately to be tempered. It took a LONG time to get to this point. It is absolutely appropriate for it to take a long time to reach a point of equilibrium again. Yes, steps should be taken now that the problem has been realized, but BABY steps. Nothing that is set in stone or potentially damaging to the kids, who are caught in the middle of a situation they didn't create. Frankly I don't care how much you're someone who wants to leap into action. This isn't the time. We try to teach kids to think about their actions and not just go with the knee-jerk response, and it sounds like you need to do that too. In your hurt, you've made it all about YOU, justifying it in your head that you put up with so much for so long. But it doesn't sound like you're adequately acknowledging that after TWELVE YEARS OF LYING, you've turned your wife's life on it's EAR. This is NOT all about you. It is finally about all three of you, maybe, rather than just the two of them, but IT IS NOT ALL ABOUT YOU!!
Hopefully the therapy helps. I find it odd that you don't like therapists when you cited your therapist's words as justification for your decisions/actions a couple of times. I'm glad you're continuing it, and I hope you're successful in keeping an open mind during it.
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack