Rob's a smart one. I guess all of Lucy's near misses were too much of a clue for him. I'm surprised that even Lucy hadn't figured out that UW was her mom after that near bike accident. Too much like her mother, I guess.
I want to say 'naughty, naughty' for keeping it from Lucy for so long that he knew (tsk-tsk Clark!), but then I realized Rob knew Lucy well enough to know she'd probably do something stupid (like expose herself to Kryptonite) if he let it slip that he was studying it. So sad that his research didn't have more positive results.
How lucky for Lucy to find her truelove in her best childhood friend. Love at first sight. Awwwwwww.
