without knowing there’s a deeper meaning to it.

Honestly I dunno if that’s necessarily the “actual” meaning behind it. (not that it can’t be the way someone technically means it, though)

You can genuinely just be saying “you’re lucky to be together with someone you love”, without also saying “I find that person you’re with attractive and want to have sex with them”

what else am i supposed to say when a friend finally gets a GF?

“Congrats, happy for you!” “You two look cute together!” “I’m glad you two hit it off!”

Don’t sweat it. Most people are fine with just a simple congratulatory statement. Doesn’t have to have any deep meaning or anything, but hey, “you’re a lucky man” doesn’t have to have a deeper meaning either.