You have nothing to be sorry for!  Vent away!   

 One of the many injustices that we have to endure is just what you've said: our closeted spouses seem to just go on as they were, while we are forced to remake our entire lives, often losing (or setting aside) friends who even when we can tell them (listen to your lawyer and do what s/he says, because your financial future may depend on it) may not believe us, or, alternately, express their sympathy for our spouses ("Oh, poor man, having to hide his sexuality all his life!") and seem to have none for us, the victims of our spouse's duplicity.  

I know what it's like to "feel like a failure."  So I'm just going to tell you that you are not a failure.  The failure belongs to your spouse, who failed to be honest about himself, to himself and to you.  Gisele Peilicot, whose husband drugged her and offered her up to other men, said, when she asked that the trial of those who abused her be made public, "Shame must change sides."  This is true for you, too: the failure is not yours; the failure is his.  

I am your age (almost 73), divorced almost eight years ago.  I can't say that I am no longer ever bothered by feelings of anger and resentment toward my ex.  I can say that whatever my ex is doing no longer impinges on my life.  I am confident in knowing that I know the type of person he was and continues to be (my ex is still in the closet), and therefore I know that he has not changed; nor is the kind of person I would have wanted to stay married to.  If I'd known what he revealed to me after 32 years of marriage before I married him, I would not have married him.  I can also say that I am grateful now to be away from him. 

[Oh, darn!  I was just editing my comment and erased a big section that I can't seem to reproduce.  So I'll just end with what I didn't erase}  You will get stronger.  The pain and anger and resentment will ease as you rebuild your life.  It will get better, and you will get better.   I know this may sound hollow and empty and even infuriating to you right now, but hold on to a belief in yourself.

 

It's really hard to keep his secret, and you're smart to follow your lawyer's advice.  

Hopefully after your divorce is finalized, you'll be able to tell your story.  And people might believe you more than you think - when I told people about my then-husband coming out, I had a few people who said they weren't surprised, and one friend who told me there was something about him that made her uncomfortable, but she couldn't quite put her finger on it (it was him sitting on his big secret). 

This is a very painful experience, and I hope you are being compassionate toward whatever you are feeling. You are entitled to all of those feelings!