Formal:
* Usted está enamorado/a. (This is the most formal way, using "usted" for formal "you")
Informal:
* Estás enamorado/a. (This is the informal way, using "tú" for informal "you")
* Estás loco/a por alguien. (This literally translates to "you are crazy for someone", and it implies a strong feeling of love)
* Te has enamorado/a. (This translates to "you have fallen in love", emphasizing the act of falling in love)
More poetic:
* Estás prendado/a. (This translates to "you are captivated" and is a more poetic way to express love)
Remember to choose the appropriate translation based on the context and your relationship with the person you are speaking to.