This guy I knew keeps looking at me with sad eyes and when I look at him he just looks away, what does it probably mean?

I knew him for about 2yrs and then smthg happened that made me be distant and be ignorant of him... after 2yrs when I met him again.. he just keeps looking at me with those sad eyes... its been a week now.. he's still the same... i can't get myself to talk and I require time.. so I find it hard to strike up a conversation and ask' u ok buddy?' I want to but I just can't at the moment.. he and I weren't even that close to begin with.. just like a classmate.. he's not at fault for what happened.. is it because he feels sorry? he doesn't need to be sorry tho..
This guy I knew keeps looking at me with sad eyes and when I look at him he just looks away, what does it probably mean?
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