When someone tells you Te quiero tanto or Te amo mucho (I love you so much), you may want to reply with "I love you more".
How to say "I love you more" in Spanish
Te quiero más.
Or:
Te amo más.
Más means "more" in Spanish.
Both quiero and amo mean "I love". There is a little difference in their use, which is explained here: I love you in Spanish.
The logical and safe way is to respond using the same verb that you have been told. For example, to Te quiero tanto you reply Te quiero más, while to Te amo mucho you reply Te amo más.
I love you even more in Spanish
If you tell someone Te quiero and he or she replies with Te quiero más, you can be playful and turn it into a mini argument by saying "I love you even more":
Te quiero aún más.
Aún más means "even more" in Spanish.
I love you more than anything in Spanish
If you want to say "I love you more than (something)" you say:
Te amo más que ...
Que means "than" in Spanish.
Some of the common phrases are:
Te quiero más que a nada. (I love you more than anything.)
Te amo más que a nada en el mundo. (I love you more than anything in the world.)
Te quiero más que cualquier cosa. (I love you more than any thing. But be careful when calling your partner a "thing".)
Te amo más que a nada o nadie en el mundo. (I love you more than anybody or anything in the world.)
I have used quiero and amo randomly. All these phrases work with amo as well as quiero and the use depends on the circumstances and the relationship.