more info needed. are you old enough to propose?

do you have the income to buy her a thoughtful gift?

yeah, you could tell her. but girls hear that all the time. like when they lose virginity. lol

i'm gonna assume you're broke and not ready for marriage...

a sensual massage. start on her back and give her a nice rub down. notice when she starts 'melting' and lean over and whisper 'i love you' in her ear. continue the massage as long as prudent, or until she takes initiative and molests you for your sweetness.

and going on from there, give her the best foreplay she's ever had. if it's memorable, so is the sweet whispers.

hope this helps.