most likely you've a mistake in your phrase, it should be: я-то представлял себе.. (note the dash between я and то). in this case то is used to specify that it's precisely you who you do speak about. that it is you and specifically you were the one who (представлял) believed/imagined/etc я то представлял себе (with no dash) on other hand means that you did imagine THAT in some way... here то refers to something that is not yet mentioned in your sentence. for example: я-то представлял тебя иначе = me, my image of you was different я то представлял себе иначе = in my mind i imagined that thing not like that я-то думал, а он нет =me, i was thinking and he did not. я то думал, а он не то = i was thinking the right thing (that one) and he was thinking the wrong thing (not that one).

“то” is used to meaningfully(emotionally) emphasize “я”

i thought i would be this.... ( but i turned out another ) -ТО- here just strengthens emotion. А я ТО, надеялся на тебя...I did relied on you( but you disappointed me) Я ТО , и не знал i did not know it at all

I agree with previous comments, especially about emphasize. Small addition: you can can also accentuate attention on some person: "Ну а он-то что тебе на это сказал?" "Ну а он-то сам что сделал, прежде чем тебя обвинять?" - you turn attention for this person, meaning, he should do smth or feel his own guilty