Adult chat website with avatars
There is a big difference between a person occasionally viewing pornography with the knowledge and even involvement of their partner to a full-blown betrayal and using adult websites to start affairs with other people.
Like many problems, it can start innocently at first, with a person visiting sexually titillating sites perhaps out of boredom or a seeking escapism but then it can escalate to other behaviours, such as directly communicating with other people online and over time can become addictive and harmful.
You might benefit from going to counselling especially if you feel traumatised and need to the help of an impartial listener to process some of the feelings.
The online medium has become a better medium for expression.