Formal:
* J'aime Jean. (This is the most common and literal translation.)
Informal:
* Je t'aime, Jean. (This is more intimate and uses the informal "tu" for "you".)
* J'adore Jean. (This means "I adore John" and expresses a stronger level of love.)
Other options:
* Je suis amoureuse de Jean. (This means "I am in love with John" and emphasizes the emotional state.)
* J'ai un amour pour Jean. (This means "I have a love for John" and focuses on the feeling rather than the person.)
The best choice depends on the context and your relationship with John.