I cannot recommend enough the following blog:

Chump Lady - Leave a Cheater, Gain a Life

There already being tons of sites devoted to reconciliation, forgiveness and cheating by mutual fault, she bases hers on three premises:

(1) You are never responsible for driving your cheater to cheat.

(2) You are not obligated to forgive or reconcile with your cheater.

(3) Your cheater is not entitled to reconciliation/forgiveness.

One warning: She does swear freely.

Here are my favorite entries:

Dear Chump Lady, I neglected him and this is all my fault

The Fallacy of "Unmet Needs"

It's not an affair! It's an act of "exuberant defiance."

{{{{{{{Vimtuous}}}}}}}