Maybe is adverb, meaning perhaps or possibly.

is a verbal construction, formed of the verb be and the verb may, which can be used in sentences like “he may be in the office today” If you were to rewrite this sentence with maybe? you would say “maybe he is in the office today” Why maybe is an adverb, you need to add a verb to the sentence ( is, a form of be, in that case)?

Maybe is an adverb, with means possibly or perhaps ; may be is a verbal phrase.

You are probably wrong. What is it?
Yes, it is true.

As per the origin, the NOAD reports that the origin of maybe is late Middle English, from the phrase it may be (that).