Offer to help him clean the pool outside or do a load of dishes for him. Get a movie from his favorite genre that you also enjoy and propose a movie night together.Or show off your video game skills by challenging him at his favorite game.
How could you hide something from them when you see them constantly?
Do sweet things for him around the house to show your interest.
Make him his favorite sandwich when you notice him staying up late studying.
You have to find out if they want company or want to come along when you go out.
It isn’t really easy to do anything without your roommate knowing.