Can "I" be the subject in a sentence?
in a sentence, 'I' is always a subject.
in English, 'I' is the nominative form of the first person singular.
when 'I' is in a sentence, there is always a verb afterwards that agrees with the pronoun 'I'.
take the sentence "I am happy today".
'am' is the form of 'to be' that is only used with the pronoun 'I'.
for all other cases, the pronoun 'me' is used. this includes 'of me', 'for me' and 'with me'.
"He told the whole story to me".
here, 'me' is the indirect object. the form 'I' cannot be used, since 'he' is the subject of the sentence instead.