They say that roughly 18 to 20% of divorced couples remarry each other, I don't know if that's strictly after an affair or other reasons for divorce. However, you can kind of guage that a bit by the stat that affair relationships mostly fizzle out after 2 years, and those that remain together beyond that continue to fizzle out over 4 to 10 years. Combine that with the fact that second marriages divorce at the rate of 60%, and that 75% of relationship affairs end, and you have an indication that even the second time around can be rougher than the first.
That's why it's imperative to grow in understanding and learning how to make love work, and eliminating behaviors and thinking that sagotages that resolve.