Others can let you know whether this is good advice but I do not think it would hurt to apologize for the fact that you did not react to her sooner. Not an over the top weepy kind of apology but a straight forward "Sorry it took a ton of bricks falling on my head for me to react!" kind of apology. Then stress that you are reacting now and that you intend to NEVER let this happen again. And make it clear that WHEN you work through things you will not let the ball drop again.
Like GEL said, she may worry that what you are doing now is short term to "lure" her back and then she will go through the same things again. A normal worry and one you can mitigate by letting her know your future intentions.
By the way, I am assuming that you intend to make these permanent changes to your life and marriage.
But what is happiness except the simple harmony between a man and the life he leads? ~Albert Camus
