Your company should have a policy about dating in the workplace. It is legal and, perhaps advisable, that your company’s policies prohibit supervisors from dating or engaging in romantic relationships with other employees of the company, especially employees who report to them. Your company can also require that spouses and family members do not work together in a direct line of supervision.
Even if these relationships are mutual, they can result in favors granted for romantic reasons, not professional ones. This is a kind of discrimination: a supervisor is basing employment-related assignments on sex, not on ability, experience, talent, or trust.
And relationships can change: after a breakup, a supervisor may be tempted to retaliate against the employee out of anger or pain.