How should I approach him?

To be honest one thing I’ve learned is people tend to do the “cloak and dagger” approach to everything and look at things more than they possibly are.

He may be looking at you because that’s how humans actually communicate, through mostly body language and eye contact. This works the same in other animals, for example, a dog or cat will “look” at a person and what they are doing, but after both eye contact happens (the person notices the viewing), the animal will then switch to either continuing to look or turn its gaze away.

So yes, you possiblu can tell that he likes you, but if I’m getting your question right you want to have a more deeper relationship thing with him? If so, just come out with it. Approach him the next time he is “looking” at you and ask him what he’s looking at, in a flirty kind of way. If he responds with a flirt back, then you can basically just ask if he “likes you more than a friend”.

If he says “No”, just move on. You’ll save yourself time nad effort if you find out soon. The worse than can happen is you get rejected, but believe me, if you “lose” him as a friend then he wasn’t a friend anyway, so it’s a simple case of “Go for it!”.