I interpret it as two people are just fucking, and both are trying to get over someone else who must have reallu hurt them. when it says "you know i'd love you is i knew you'd let me down" just shows his cynicism towards love-he loved someone and she let him down. and that person is all he is thinking about in this new relationship and he knows they are using eachother, so he just wants to get out of it.
I interpret it as two people are just fucking, and both are trying to get over someone else who must have reallu hurt them. when it says "you know i'd love you is i knew you'd let me down" just shows his cynicism towards love-he loved someone and she let him down. and that person is all he is thinking about in this new relationship and he knows they are using eachother, so he just wants to get out of it.