A new study says the top reason for divorce is not cheating on one's spouse. In fact, adultery is down considerably. Divorce is horrible by any stretch of the imagination. Arguably, couples who marry don't enter into Holy matrimony with the end in mind; they have feelings of living happily ever after.And oftentimes, the main culprit divorced couples give is being unfaithful during the marriage. While a spouse's cheating ways still rank high on the list, takes a backseat nowadays.Research conducted by the Cooperative Legal Services, using over four decades of data, suggests that the main reason divorced couples say they split today is over behavior that is less than reasonable. It's the excuse often seen in Hollywood splits. Ever hear of "irreconcilable differences."Examples are when man or woman tightens the grip on their spouse when they express desires to hang out with friends. Study authors say this is due to, perhaps, anti-social behavior from the stern spouse.Another example of "unreasonable behaviors" as a main reason for divorce is when one spouse is dipping too much into the family's piggy bank for risky investments, pleasure or other things they disagree over.Another noteworthy discovery was made from the divorce study: only 15 percent of couples end their marriages today versus a whopping 47 percent in the '70s.