Always when my boyfriend is gone for a few minutes, I HAVE TO ckeck his internet history to see if he watched porn. I know he does tht, a lot!!! He doesn't keep it a secret for me, but I still have the urge to check it behind hi back... Is this normal?

You should get married immediately!!!
It' bad, it's really bad. You show that you don't trust him and if he finds out, he'll probably be pissed. I know I would.
You're worried though, I can understand that. You wanted to know what he was doing instead of studying and talking to you, and you do. So there's no need to look anymore, is there?
Just stop it. You found out what you wanted, end of story.
Confront him about his exams though, and the games.
Like, don't get mad. But sit down at a proper time with him, look him in the eyes, and tell him you're worried about him. Then see how he responds.
You CHOOSE to snoop.
If you really want to handle this like an adult, communicate with him. I don't mean "beat him up over not paying attention to you" but actually talk to him and LISTEN to what he has to say too.
If your answer is to just snoop and violate his privacy then... you lose ANY right to complain about what you find. If he turns against you or gets mad at you for this... you will have earned his distrust.