Friend gone to uniWatch
You could contact him using social media. Even video chat would allow you to see him without being fined. Is it in an area where you could maybe meet up in town? That way you could see them but then it would not be illegal.
All the best.
There are plenty of ways to keep in touch with them, but whilst it's OK to say you miss them, don't go on about it and make it all about you. People and friendships change and mature, so you couldn't have kept that idyllic summer going on and on.
Finally, respect the rules that are in place for a reason. It's not worth your friend getting into trouble at uni for a bit if time socialising with you, or the pair of you spreading coronavirus to other people, including those in his accommodation, who could be vulnerable or have family who are.