Imo it's normal to feel insecure about this, especially given the tales you hear about uni! The best thing you can do is communicate how you feel to him when you feel insecure - if he isn't an *******, he should reassure you. Focus on yourself and your hobbies to take your mind off worrying about him, too.
You have to trust that he loves you enough to not go and fool around, which can be very difficult for some people but that's all you can do. I would only be worried if he stops communicating with you or seems unenthusiastic about it.