Fallacy of Begging the Question.
Thomas' words to Jesus in Greek literally read, "the Lord of me and the God of me." In Greek this is how one would refer to two persons. If one wanted to refer to one person he would say, "the Lord and God of me." This is confirmed by the first and Sixth Granville Sharp rules. However, Trinitarians make a convenient exception to the sixth rule for this particular verse.
Both nouns, (1) Lord, and (2) God, are each qualified by the definite article ('the'). Both nouns, (1) Lord, and (2) God, are qualified by the words "of me." This is also telling. Thomas could have said, "the Lord and the God of me." But he did not.