"The Angel's last Mission"

The Angel's last Mission is a teen fantasy romance series about an angel who has no choice but to become a human after unintentionally saving a male student in danger. The now-mortal angel then interacts with teenage high school students and learns about love, friendship, and what it means to be human.
An angel, wishing to understand humans more fully, accidentally becomes one herself in an attempt to intervene in a suicide attempt.