I don't think this song is difficult to understand at all (but of course everyone is free to make their own interpretation). Go backwards: there was a woman he knew, who had something he needed but she left, and when she left he died. He wasn't always a loner, he lost a girl who he was in love with OR was infatuated with, in any case losing her destroyed him emotionally. Now, regardless of whether he wants to get her back or replace her, dwell on it or move on, the only thing he's capable of is carrying on his life in solitude, looking at other people and judging them. He may merely be projecting his own expectations on them, or it may be that he has developed a knack for seeing who people are underneath their appearance (because he found out the hard way who the woman he loved was underneath). In any case, he is no longer a social person and when you see the loner you should just let him be. He already knows who you are.
I don't think this song is difficult to understand at all (but of course everyone is free to make their own interpretation). Go backwards: there was a woman he knew, who had something he needed but she left, and when she left he died. He wasn't always a loner, he lost a girl who he was in love with OR was infatuated with, in any case losing her destroyed him emotionally. Now, regardless of whether he wants to get her back or replace her, dwell on it or move on, the only thing he's capable of is carrying on his life in solitude, looking at other people and judging them. He may merely be projecting his own expectations on them, or it may be that he has developed a knack for seeing who people are underneath their appearance (because he found out the hard way who the woman he loved was underneath). In any case, he is no longer a social person and when you see the loner you should just let him be. He already knows who you are.