commitment-phobic
/kəˌmɪtm(ə)ntˈfəʊbɪk/adjective
Characterized by or exhibiting resistance or aversion to the commitment involved in a long-term romantic relationship. Now also (more generally): exhibiting resistance or aversion to making a commitment to any decision, course of action, etc.
noun
A person who is resistant or averse to commitment, especially in a romantic relationship.
Origin
1980s; earliest use found in The New York Times Book Review. From commitment + -phobic.