I think you are insecure and unsure of your ability to relate intimately.
Why did you snoop and look at his computer? Was it really any of your business? Did this stuff you found out occur while you were a couple or, was this prior to his meeting you?

There are some things in every couples life that are private to each individual. For instance, my wife doesn't know the content of what i discuss with those I counsel, but she knows I counsel people. I don't know the daily interaction she has with men in her day to day work or, to what extent she counsels them. We both have many hours of relationship counseling. We have been married 35 years.
The issue here is trust and allowing the other person to have a private life. It is good to have a little mystery about each other.
Now, if that mystery is that the other is leading a different life and is doing things that are not acceptable, then it is time to talk about it and try to resolve it.

Does he know you snooped and looked at his computer? If not then when you confess it to him you should be ready to accept the consequences for the action you took.

Good luck to you,