Wow... Many options.
Thanks, in special to Donay Mendonça
He gave me the idea that best fit - though some changes will be required to my specific case (because the sentence "Ahh... Quanta saudade em seus olhos!" was about a writer speaking of a character (who was missing his beloved long gone).
Then, I decided to do:
"Aww... By the look in his eyes, it was possible to see how much he missed her!"
But I also think it is possible to use:
"Aww…. There was a glare of nostalgia in his eyes!".
Coments are welcome.