No one has a manual on how to navigate infidelity. Your W may not understand that honesty and truth are crucial to choosing you. I expect that she's ashamed of herself, and not coming clean helps mitigate her shame.
The problem is: coming clean is just the first step in the WS's healing. R works best - and may work only - if the WS changes from cheater to good partner. That requires a lot of digging for your WS and probably therapy, too. Many WSes won't do that work. She may have to figure out why she responded to her HS crush. She does have to figure out how not to respond in the future. (Some people can replace dysfunction with good function without figuring out why they malfunctioned.)
Your thoughts and feelings are pretty normal for a BS. Being betrayed is a trauma. For most, the first response is shock, and that's a condition that's not conducive to clear thinking.
Focus on yourself. What do you really want, besides getting off the roller coaster of shock and healing? Sure, 25 years is a big deal, but what about the next 25 years? Do you want to spend the rest of your life with your W?
If you do, what are your requirements for R? Your best approach is to decide what behaviors will show you your W is a good candidate for R. But R is a cooperative endeavor - your W may have requirements, too. A successful R requires building an M that serves you both. If your mutual requirements aren't compatible, you can shake hands and split (close to) amicably.
I think it's very healthy to realize your W is not doing the work necessary to rebuild your M. But, you can't control her; she has to choose to do the work. What if she never does it?
If your W doesn't come clean, are you ready to D? You have to make your own decisions to act, but I strongly recommend not laying down an ultimatum until you're ready to impose the consequence if your W doesn't comply.
If you're not ready for an ultimatum, so be it. Act in your own best interests. Sure, you have to respond to what your W does, but do so always with your goal in mind. When you have to choose an action, choose the action you think will get you closer to your goal.
At this point in your recovery, I urge you to put aside the question of D & R; instead focus on your own healing. Process the anger, grief, fear, and shame out of your body. That will clear your head so that you can perceive reality accurately and make the optimal decisions.
No matter what, the BS heals the BS; the WS heals the WS; if you both want to, together you build a new M. That means you can heal even if your W doesn't. And it means you can heal even if you D.
Have faith in yourself to heal. I know you feel awful now. Just remember that's temporary, if you do your healing work. A good IC can help.
Clear your mind and body. Perceive. Assess. Act. Monitor. Adjust as necessary. You know you're successful when you find your way to survive, first, and then to thrive.