You are right. Biblically, you are not commanded to divorce. You have the right if she commits adultery. If you have proof that she has, then you need to decide what you want.
If you want to save the marriage and forgive her, then you'll need to DB like hell. Again GAL is what will attract her back to you. Detachment is first, for your sanity, second, it's a seductive trick..if you are a little mysterious, interesting, having a great time then she'll begin to wonder...hmmmm...maybe this guy is interesting.
If you want a divorce, and only on biblical grounds, then I suggest you get evidence of the affair. This will be necessary if the divorce is contested. Then talk to a lawyer. But be careful, divorce lawyers will promise the moon, only to jack up the litigation and raise their fees. DO you want shared custody? Do you want your kids partially raised by the man who stole your wife? I know those are painful questions to ask. But that's what you are going to have to think about if you want to divorce her.
I suggest you get evidence of the affair anyway. It seems that if your wife is holding her cards close to her chest, she's probably already positioning herself regarding money, finances and custody in as advantageous way as possible. Get the evidence even if you don't use it/
On the other hand. If you are trying to save the marriage, perhaps you are wondering what does a 180 look like in your situation?
Seriously, try and GAL..do things for you. Have fun. Guy night, the gym, a hobby, etc. And keep that up regardless of what happens. This will make you strong. 180 or no 180, at least GAL. What makes you happy? And don't picj GAL activities thinking about their effect on your wife. GAL is for you. It's different from a 180. If you are happy and full, it might attract her. A 180, onthe other is behavior that might shift the relational dyanmic around. Sometimes GAL is a 180, but not always.
Then, as Michelle suggests, keep a journal of your techniques and their effectiveness. Keep trying new things. Give the techniques a few weeks.
But, my friend, as she continues to be cold and hard, and selfish, you feel the love slipping from your heart. That's what's really killing you. You can't wake up or sleep without this freaking situation consume most of your thoughts.
Again GAL trues to help with that. It takes your mind off it. GAL is a way for you to lose yourself in a task and have fun. And bro, you need the fun.
180 is a calculated behavioral change that is very focused on your wife's response. I think GAL is a pre-requisite for a 180, it gives you the strength to do it.