I can't believe that Jimmy wouldn't figure out that CK=SM when he notices how well Clark fills out the Suit. Also, if Lois told Jimmy that Clark-in-the-Suit was kissing her, doesn't Jimmy wonder why he thought Superman was kissing Lois?
But then again, Jimmy isn't the sharpest crayon in the box.
OR...
He did figure out that CK=SM and has decided to keep quiet about it.