'Serving' is a verb here. It is used in the present continuous tense with the modal verb, 'may' so the auxiliary verb 'be' is in the root form. Let me illustrate how this tense is used.
My behavior is serving me. (present continous, affirmative)
My behavior is not serving (present continuous, negative)
My behavior may be serving me. (present continous, affirmative with modal verb)
My behavior may not be serving me. (present continuous, negative with modal verb)