I am looking for a word, or a phrase, in any language that means
something to the effect of:  "thank you for your incredible
thoughtfulness, I care for you."  The english phrase "thank you" seems
so formal.  My boyfriend and I are looking for a word or a phrase that
we can say to the other after the other has done something thoughtful,
or kind or considerate.  We're looking for a warmer, more caring way
of saying "thank you and I care for you."  Does a word or phrase like
that exist?

I like the Spanish word for "thank you," "gracias," which is related
to "grace" and "gracious."

"aloha mahalo nui loa" -- this is Hawaiian. Aloha means love,
compassion, kindness. Mahalo means thank you. Nui means great. loa
means very. The way this phrase is given to you here is the way Hawaii
residents would express the feelings that you want to express. A
Hawaiian expression like this is very spiritual, like a prayer, and
invokes "mana", which is the Hawaiian word for spiritual power.
Pronunciation of Hawaiian vowels: a as in father, o as in pole, i is
the ee sound in seen, u is the oo sound in moon.

It is rarely used today, but still some decades ago, the phrase "Gott
segne dich" (or, in a respectful form, "Gott segne Sie") was used in
some regions of Germany to express "thank you". It translates as "God
bless you".

Scriptor

Namaste. Not exactly "thank you" but it definitely captures the "I
care for you" aspect of your question.

http://www.exoticindiaart.com/article/namaste
Namaste - The Significance of a Yogic Greeting

The gesture (or mudra) of namaste is a simple act made by bringing
together both palms of the hands before the heart, and lightly bowing
the head. In the simplest of terms it is accepted as a humble greeting
straight from the heart and reciprocated accordingly.

Simply put, namaste intimates the following:
'The God in me greets the God in you
The Spirit in me meets the same Spirit in you'

THANK YOU, Gracias, Aloha Mahalo Nui Loa, Gott Segne Dich, and Namaste
to all of you for your suggestions on my question!  Although I have
not received an official "answer" from the powers that be at Google,
your comments and suggestions are wonderful.  Thank you all!  I
appreciate your suggestions.  Have a great weekend.