"Eu te amo"
Here's a breakdown:
* Eu: I
* te: you (informal)
* amo: love
Other options:
* "Amo-te" - More poetic and less common in everyday speech.
* "Eu amo você" - More formal, using "você" instead of "te" for "you."
The best choice depends on the context and your relationship with the person you are speaking to.