That comment he made is far too vague to read into his happiness in his relationship. I think you are being a little presumptuous perhaps? Did he ever admit to having feelings for you? If not, I don't know why you're hitting on someone else's man.....just because you're single it doesn't mean you're free to go 'innocently' putting vibes out there and trying to break up someone's relationship.
I know if some girl left a note like that on my fiance's car, they better pray I don't know where they live.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi