abandoner
n. countable C2 Proficiency aban·don·er
n. someone who leaves a person, place, or responsibility behind forever. You use this to describe a person who quits or gives up on something they started.
n. a person who deserts or leaves behind a person, duty, or cause. Often carries a negative connotation of failing to fulfill a commitment or moral obligation.
He was labeled an abandoner after leaving the team mid-season.
The child felt like an abandoner when she finally moved out of her elderly parents' home to start her own life.
Sociological studies of the era often categorized the father who left his family not merely as a runaway, but as a systemic abandoner of civic and domestic stability.
From abandon + -er.