Try to convince her that even if she is determined to divorce, she ought to be determined to do it the right way. It is to be hoped that your marriage can be saved, but at least try to save yourselves as much future heartache as you can. How? Talk. Listen. Reflect. Learn. Repeat, repeat, repeat. The vast majority of couples need help to do this, but you two will be doing the heavy lifting. It is well worth doing.
I think it is in your best interest to move things out for the time being–you heart is too wounded to be as generous as you would like to be–and it is your right to sever the common conjugal life when you have been the victim of infidelity. Still, it is in the best interest of both of you to at least try to figure out what caused the wheels to come off. Maybe your suspicions are correct, but it is better to know.
I say this because I know too many divorced people who have “I wish I had known then what I know now” stories to tell. WAY too many. Some would still be married, some not, but again and again my divorced friends and relatives report that they would have avoided a lot of mistakes if they had stopped and looked at how their lives had gotten to the point they had before they divorced. They’d have an easier time forgiving their ex, too. More to the point, they would have been less likely to have gotten into a subsequent relationship with all the same fatal flaws as the first one. This work is best done by both spouses together, because you each hold pieces to the other one’s puzzle. So while you may be very wise to consult attorneys and have a legal separation to protect each other’s financial future, you would also be wise not to fail to have some very deep talks with the one person who has more of the answers to the questions that your futures will pose to you than most of us can ever appreciate.
Sometimes, this talking saves a marriage, but even when it does not, it can save a lot of future heartache. I’d present this to yourself and to your wife in those terms. When you are done, you’ll have a very good idea, too, about whether or not you will have a cause to petition for a decree of nullity, if you do go through with a divorce. Who knows? You may even save your marriage. Few people realize how costly a divorce is, how much it takes out of both heart and bank account. Do this work; you owe it to yourselves!