How do you say i love you very much in spanish?

Answer:

Nena, te quiero mucho.

O

Te quiero mucho, nena. Te quiero mucho bebé or Te amo mucho bebé, however you wouldn't say it that way. You would say, "te quiero mucho, mi amor". Or "te quiro mucho querida".

The above answer is correct, however nena is an infant and it is not used in the sense of "I love you baby"

The Word 'nena' is a correct slang usage in Spain.