SafeSport doesn't apply to this situation, but I still think the SafeSport rules explain this well:
"An imbalance of power is always assumed between a coach and an athlete, regardless of age, and an adult in a position of authority... Once the unique coach-athlete relationship is established, the authority and trust on the part of the coach over the athlete shall be assumed, regardless of age. Factors relevant to determining whether there is an imbalance of power include, but are not limited to: the nature and extent of the adult coach’s, official’s, director’s, employee’s, parent/guardian’s or volunteer’s supervisory, evaluative or other authority over the athlete; the relationship between the parties; the parties’ respective roles; the nature and duration of the sexual relations or intimacies; the age of the adult coach, official, director, employee, parent/guardian or volunteer..."
An eighteen year old can believe with all of her heart that she's in a healthy, consensual relationship with her married coach who has partial control over her scholarship and role in lineups and who is (presumably) literally responsible for her safety when spotting her or assigning her skills, but that doesn't mean it's actually a "consensual" relationship. Coaches who engage in sexual abuse/misconduct in this pattern - married, at least 10-15 years older than their very young adult athletes - are often manipulative and emotional abusive: they coerce and convince their young athletes to enter into a "consensual" relationship after grooming them. And sometimes an athlete believes she's in a consensual relationship with her coach and then she tries to end it... and discovers it's not as consensual as she thought. And often those coaches use the athlete's sport against them, telling them that if she ends the relationship, he'll make sure that will end her involvement in her sport or she can't be successful without him, etc.