Reading your letter, I can understand that you're in a very difficult place. You've completed eleven years of marriage, have two children and an entire lifetime of memories to show for it. So how do you resist the temptation and endure something that leaves you in want?
Both of You Have Changed
It seems that the two of you were very different when getting married, and understandably have changed over the years, to a point where there is little understanding. I can see this from the difference of opinion in your letters.
There is a saying that being in love is two souls wrapped in one body. My parents completed 30 years of marriage and I can honestly say they shared that sort of intimacy. Over the years, as in any marriage, they settled into a routine that was not befitting the blush and flutter of romance and the fire of intimacy, but given the choice, they knew they wanted to be with each other, and this, to me, is the key to your answer.
Decide If You Want to Work It Out
You need to ask yourself whether you are willing to stay with Cabby and exercise that choice by trying to work things out. From your letter, it seems that, while Cabby is an excellent provider and good father, you feel neglected. It seems that you had settled for this way of life until events before you forced you to consider the quality of your marriage.
I can't see you staying in your marriage the way it is and enduring temptation because it will eventually make you very unhappy. I don't think you should end your marriage either.
Tell Him You're Not Blaming Him
I think you and Cabby need to sit down and talk, no matter how uncomfortable it is. You need to tell him how you feel in a way he would understand. Appeal to him that this is not about blame, but about trying to save something. The two of you need to ask yourselves what you want of this marriage and how that could be met. I would give your marriage some time, perhaps a year, to see whether your wants can be met, all the while working towards trying to achieve that.
Try Your Best Before You Call It Quits
I really do understand how you feel. I've woken up one day and discovered that gap, and agree that its very hard to rediscover what was once there. But we all feel a sense of loss at the end of a relationship, a feeling that, if only things were different. I would want you to give yourself every opportunity to try and make your marriage work, so that if it's quits, then you know you tried your best.