weakhearted

/ˈwikˈhɑrtɪd/
adjective
  1. Lacking courage, determination, or emotional strength; easily discouraged or frightened.
    • The weakhearted soldier fled from the battlefield at the first sound of gunfire.
    • She called him weakhearted for giving up on his dreams so easily.
    • It's not a job for the weakhearted; you need to handle constant rejection.