I had to agonize for a very long time before I could finally make the decision to divorce. We didn't have an immediate crisis like cheating to spur me to move faster. Soooo many factors weigh into the decision. Like: What is the quality of your relationship otherwise? Is the cheating an aberration in what is otherwise a decent marriage? Or are your girls being exposed to daily anger and unhappiness and a poor example of how a man and woman should treat each other (even before the cheating)?
I agree with the previous posters that counseling, thinking about it, etc. etc. is crucial. But if the affair has thrown your marriage into a crisis, it might be a good idea to do that thinking and soul-searching while separated. If you file for divorce and get temporary orders, there is nothing that says you have to go through with it if you change your mind later. I think you have a year. You can spend that year in counseling, with and/or without your husband, and really think it through.
That's just one option, anyway.
And -- just my two cents' worth -- there is a ton of research pointing in BOTH directions when it comes to the effect of divorce on children. It's a hard kind of research to do without underlying bias in one direction or another. I have zero doubt in my mind that my kids are better off with their dad and me apart. I used to wish my parents would get a divorce because they were so miserable, and I had no positive, happy parent in my life showing me how to really live. Each situaton is SO individual. Again, counseling helps.
If/when you do decide to file, I highly recommend Andrew Passons. He handled my divorce, and was very sharp, compassionate, and professional. His contact info. is:
Andrew J. Passons
Law Office of Mark Lewis
509 S. Carroll Blvd., Suite A
Denton, Texas 76201
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###-###-#### - fax
Good luck to you. You WILL get through this, and your girls WILL be OK! Hugs :)