commitment phobia
/kəˌmɪtm(ə)ntˈfəʊbɪə/noun
Resistance or aversion to the commitment involved in a long-term romantic relationship. Now also (more generally): resistance or aversion to making a commitment to any decision, course of action, etc.
Origin
1980s; earliest use found in The Washington Post. From commitment + -phobia, perhaps after commitment-phobe or commitment-phobic.