Do not tell him at all. It's for him to find out.
Try the following first before anything else:
1) Join him for study at the library. Then you will know if his
study mates are all guys, all girls or mixed
2) If it's an all guys or mixed group, join in, wait and watch for
his interaction within the group. If it's an all girls groups,
excuse yrself from the study group. Don't join in.
After the event, you'll have a much better idea of how to proceed
next.
Report updates and I'll advise on what to do next.
Good luck!
