Formal:
* Ryan, je t'aime. (This is the most common and literal translation.)
Informal:
* Ryan, je t'adore. (This means "I adore you" and is a more passionate expression of love.)
* Ryan, je suis amoureux(se) de toi. (This translates to "I am in love with you" and is a more poetic way of saying it.)
More casual:
* Ryan, j'ai un gros crush sur toi. (This means "I have a big crush on you" and is a more playful way of expressing your feelings.)
Remember to choose the phrase that best fits the situation and your relationship with Ryan.