It doesn't seem as common thesedays as it was in past generations. People aren't so prepared to Marry young any more. Often people date several people over the years, even at the same time sometimes, until they find someone they feel that they can be seriously committed too, and even then there's no guarantee that either partner won't cheat. Some people even agree to 'open relationships', and it doesn't seem to be a big deal now a days.
People dont tend to take the word monogomy as a devoted and serious one, however in saying that monogomy isnt part of the human genetic make up. Its sad that people dont take their vows to one another seriosly anymore, its even sader that they hide, lie and cover it up.
so in conclusion no i dont think people thake monogamy seriously at all anymore.