Thank you for the additional info. The good thing overall is that she is willing to work on the marriage, so that means all hope is not lost, at least when it comes to second chances. The more important question or issue is to decide if you are truly willing to work on your marriage or if you will cheat a third time. It's understandable that after 13 years, a relationship could lose the initial spark, but there had to be a spark there to begin with that made you marry each other. Try and remember the things that attracted you to he in the beginning, remember that everyone ages and changes. Ask yourself;
What have you done to make her feel special, to keep the spark and passion alive in your marriage?
What do you think would happen if you put all the energy that you put into this other woman, into your wife?
Does she feel like the both of you could do more to work on your marriage?
Do you take time out a few times a month to spend alone time with each other?
Do you buy her gifts (no matter how small), surprise her ever, or do unexpected things out of your ordinary schedule?
A marriage is a two way street, its the responsibility of both people to put in their fair share of work towards it. Yes, I said 'work', because many people think that marriage is something that exists on its own, but I want you to think of it more like a garden. Left untended, you garden can become a barren wasteland, but tended to with love and care, it will blossom and bear fruit.
You have this one chance to make things right with your wife. She forgave you once, and is now willing to forgive you again. This is not the way things usually work, what if she was to turn her back now and not ever take you back, what would your loss feel like? Is it worth taking that chance again? You are who you choose to be. Your actions will always speak louder than your words. You choose what happens next in your life and how your marriage fares after this blow.
Therapy is good, for you and as a couple. Maybe you can get to the bottom of what you are so dissatisfied with and make changes in yourself and your marriage. The helping hand we look for is sometimes at the end of our own arm, and you can take the first step to making things right if you want to.
I welcome your thoughts, let me know if you want to talk more