Please don't tell him he's cute, his brain would short-circuit so hard and he might just die of combined happiness and embarrassment. (By which I mean: absolutely do tell him sometimes, because it would be hilarious.)

"That's amazing..." That she won't age, he means. He says it unthinkingly, but having said it, he starting feeling it, a bit more than he probably should. Everything is so warm and fuzzy right now! "That is: you look -... I mean..." Argh, he can't just call her beautiful, right?! That would be rude. Or at least weird? Maybe both...

As to the Chevaliers protecting her: "That sounds like a good thing, though!" He's not sure why she'd enjoy being away from people like that... but then, he's not about to pry, either. "Well, there's something to be said for freedom as well."