To me this song is about being so deeply in love with someone that you son't see their faults or just don't care about them, but then when you're 'blind to all the same old thoughts' meaning no longer in love, you see what they're really like and you're no longer under the illusion of the other person being saint-like.
Also, since the lines go 'I'm under no illusions NOW' i'm thinking the loved person might have done something mean, and this is why the narrator's eyes are finally opened.
To me this song is about being so deeply in love with someone that you son't see their faults or just don't care about them, but then when you're 'blind to all the same old thoughts' meaning no longer in love, you see what they're really like and you're no longer under the illusion of the other person being saint-like.
Also, since the lines go 'I'm under no illusions NOW' i'm thinking the loved person might have done something mean, and this is why the narrator's eyes are finally opened.