Mohammad E. answered • 06/20/19
Four Years of Language Training
Interesting question.
In other words, you have to determine if you need a subject I or an object me,
Before delving in, on a side note, I prefer strongly against using the word that. It is a clue to unspecific or ineffective word choice. Rewording the sentence to exclude that gives each word more weight and reduces unneeded words.
On a second note, remember that English is essentially an amalgamation of foreign vocabulary, Germanic roots, and Latin vocabulary shoved together and evolved within the last millennium or so. Just because a phrase or sentence is grammatically correct doesn't necessarily mean that it sounds right and just because something sounds right doesn't mean it is the most correct.
Take the classic sentence The horse raced past the barn fell. This is a grammatically correct sentence, but it doesn't sound like it makes sense, Is the horse falling or is the barn falling? You will find that the sentence is an example of one which follows all of the grammatical conventions, yet, it does not sit right in the ear.
Back to your question, the verb in your sentence is is which is a linking verb, and a linking verb equates the subject to another form of the subject.
Think of Aladdin when the cave mouth asks "Who disturbs my slumber?" The hero's response is "It is I, Aladdin." Likewise, the correct of your two sentences is It is only I that am confused.
When who refers to a personal pronoun, the verb is conjugated to match that pronoun
It is only you who are confused.
It is only I who am confused.
It is only he who is confused.
It is only they who are confused.
To prevent confusion and to ease the reader's/listener's poor ears, consider rephrasing.
