NOT A TEACHER
Hello, Tufguy:
I often hear American speakers say something like "This secret is just between you and I."
You, however, will never make a mistake like that if you memorize one easy rule: After a preposition, you ALWAYS use the objective form of the pronoun.
You know, of course, that "me" is the objective form of "I."
Thus:
"Mona said something about Tony and me / her / him / us / them."
"Mona gave a gift to Tony and me."
"Mona baked a cake for Betty and me."
"Mona received a gift from George, Susan, and me."
"Mona graduated from college after him, her, and me."