Maybe vs. May be

The difference between Maybe and May be is that the single-word term maybe is an adverb, which can never be used as a verb even though it contains the modal verb may and a verb be. The double-word term 'May be' acts as a verb phrase just like should be, can be, could be, will be, etc. 

Maybe is an Adverb

We can replace it with perhaps/most probably. 

Example: Maybe I was wrong.

            Incorrect: I maybe wrong.
              Correct: I may be wrong. 
              Correct: Maybe I am wrong.

                  

May be is a verb phrase

'May' is a modal verb, just like can, will, should, must etc. We use 'may' to mean possibility'. And 'be' is the main verb, which means becoming. We can compare the function/syntax of 'may be' with can be, could be, might be, should be, etc. 

Example: This year may be lucky for me. 

         Incorrect: May be this year is lucky for me.
            Correct: Maybe this year is lucky for me.
            Correct: This year may be lucky for me.