It's just down to the way the two verbs/phrases work. "pretend", in the relevant sense, is followed by a to-infinitive: "I pretend to be normal", "He pretends to like opera", "I pretended to agree ", etc. "go back to", in the relevant sense, is followed by a noun or noun phrase, "I go back to being me ", "I went back to my house ", etc.
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nospaceto be normalHere "to" is part of an infinitive structure (to be).
nospaceI go back to being meHere "to" is a preposition. The -ing form of a verb (being in this case) is used after a preposition.