Estefania:

Please refrain from using sentences like "please help" or words like "translation" in the header. We all need someone kind enough to make things clear for us, and using those words makes your post less relevant. Instead, try to use the words or the sentence that is giving you trouble and then use the post to explain how it was used, or what it is about it that you don't understand.

Regarding your question, "mi corazoncito" could be an equivalent of "my sweetheart," "my darling," etc. However, since he is using the possessive and the word for heart, it probably means that he wants you to be close to him and he loves you as his own heart.

I hope it helps!