It can be detrimental to your real world relationship and change the way you relate to that person. It is something to think about before you get too deeply involved with an on-line affair. Some are not. People with problems in their marriage may find the cyber-love hastens the demise of the marriage. It may be the catalyst that finally brings everything to a head.
Marriages have been know to break up over on-line relationships.
Each person has to deal with that question individually. Many people who care very much about their marriage, still find it hard to give up their cyber-relations. People have different ways of coping and for rationalizing. However, it is a vast cyberspace out there and relatively easy for people thousands of miles apart, with many time zones separating them, to be online without each other and to meet new love interests. The promises people make to each other online are usually given and taken very seriously.