To cheat or not to cheat

Who says when you are married it is forbidden to have feelings for someone else? This friend of mine is married and happened to see her first love. This person transforms her to another person, a person from the past. She was wondering... Why would it be bad to kiss him just for this time and live an intense moment? It doesn't mean she will have a divorce to be with her husband neither she will continue to see this other guy. It will be only this moment. It would even renew her marriage if  the husband doesn't find out of course.

What is the right thing to do? What is right or wrong is very subjective. I dont't really know the answer to this. 

I could only say that there is a price for every desicion we make. So I am guessing that if she
shows temperance and stops before she makes any move further with this guy from the past, she will be rewarded from karma and have a better relationship with her husband. I see it as a test in her marriage to confirm her choices. The choices we make in our lives face obstacles that if we overcome we go closer to our goal. On the other hand if she makes this move, she would have to face some problems that would magically come up in her marriage (it could be a relationship, it does't matter). 

If you have any ideas let me know..