I understand how you feel, it’s a huge problem in our world and easy to keep hidden but if you’re in a relationship it can most assuredly cause problems. Some believe that they aren’t being unfaithful because they don’t have any physical contact with others, this not true. It’s been a source of addiction for years and can most definitely break down your relationship, the addiction can and will get worse with time, it works the same way as any addiction. It might get difficult for you now that you are aware of it but how do you deal with it, if you start monitoring him he may become more sneaky and find ways to keep it from you, desperate people do desperate things. I think that you should bring it up in the open and suggest counselling perhaps for both of you, it’s still a helpful choice for you and him, there is usually reasons why people can get addicted to this and therapy is a good choice to get better results.