Relationship friction, duty and responsibility, loss of control, power struggles

Many romances have obstacles and stumbling blocks that keep them from thriving. For clarity, this entry will only explore relationships being affected by forces outside of the couple's control.

An interfaith couple being blocked by loved ones or members of their religious communities
Teens being forbidden by parents to pursue a relationship 
The character's wealthy family disapproving of a love interest from a humble background
Children of feuding families struggling to make a romantic relationship work
A royal being discouraged from pursuing a love interest who is beneath their station
Loved ones discouraging a character from pursuing an unhealthy or toxic relationship
Parents with deeply ingrained bias (involving race, sexual identity, etc.) forbidding the relationship

The couple having to sneak around to be together
Joining a romantic partner's family, culture, or religion and causing strife with their own family
Tension with family members
Having to lie and keep secrets
Not knowing which family members to trust with the truth 
The couple having to come up with creative ways to communicate, such as sending letters in code or using burner phones 
Family tension bleeding into the romantic relationship, causing friction and conflict
Being asked by the partner to change in order to be accepted into their family
Being guilted by loved ones to respect the family's wishes or adhere to duty