Because you took him back, and he agreed to change his behavior of web cam porn, you have to find a way to forgive him and trust him unless proven otherwise. Forgiveness can be extremely difficult, as can trust, but if you can’t find those two things in your heart you shouldn’t be with him.
Allow yourself time to work through these emotions. The distance between the two of you is going to be difficult because dating someone at a different university, even without the past issues you two have, is often fraught with mistrust.
Keep your own life active and full. Remind yourself of why you forgave him and took him back — over and over. And understand that each day that passes where he does not do what he’s promised not to do is a day of progress and commitment towards your relationship.
This is an “inside job” you have to do on yourself. Keeping the communication open with your boyfriend is good, but if you make this an issue when it isn’t one, the ghost in the relationship will destroy it. Let go and forgive.