Divorce is like a freight train, experts say. But while most everyone sees the faint light in the distance long before its iron chassis and churning wheels are right on top of them, many like to ignore the impending end and convince themselves that the light is really nothing.

“There are always signals but you may not understand them,” said Bonnie Russell, a Del Mar, Calif., divorcee and owner of a professional referral service, who has her own experience with the topic. “You bump into people and they aren’t as friendly as they normally were. You think, ‘That’s odd,’ but looking back, you realize that they knew that your spouse is having an affair. You may not know that they are cheating on you but everyone else does.”

While many marriages end because there was an affair, research varies on just what percentage of divorces are the result of an extramarital relationship. A common percentage cited is 20 percent, based on 35 years of research conducted by John Gottman, Ph.D. But psychiatrist and former columnist of Psychology Today, Frank Pittman’s findings from a 1997 study, point to a much larger percentage: 50 percent.

Several marital attorneys who have a steady diet of divorce daily agree that the number of divorces they litigate due to infidelity is larger. “Probably it’s more like 60 percent have had affairs or are having affairs. But that’s anecdotal,” said Dawn Cardi, a matrimonial lawyer of 28 years, currently in private practice in Manhattan. “I find they will blame the affair for the breakup, but often the affair is the catalyst or the symptom. And  when I speak to the parties, I find they say this marriage has not been functioning for a very long time, long before the affair.”   

When an extramarital affair is the precursor to a divorce, the signs leading to divorce can be a little bit different, according to some experts, often adding a dimension of secrecy or outright lying to the mix on the part of the spouse who is cheating. 

But overall, most agree that the following signs are indicative that your marriage is ripe for ending.    

1.  A fall off in frequency and quality of intimacy.
“There is a definite lack of interest in sex and they don’t communicate about it and don’t do anything about it,” says Cardi. “Or they are in very different places on it. Basically, the trigger is that sex is not working and hasn’t worked in a while.”    

2. Fighting or bickering more frequently than in the past.
According to Lauri Puhn, a family and divorce attorney-mediator in New York, N.Y., and author of “Instant Persuasion” (Penguin), the arguments are redundant and never get resolved. “It’s the about the same topic over and over again,” she said. “You are arguing over the same issue and it increases in frequency. And there is no resolution. It doesn’t go anywhere.”