The support service then launched an investigation in 2019 and mid-way the man resigned from the company.
The couple continued their relationship until the man claimed the woman's family put pressure on her to leave him claiming he was only after her money.
He broke up with her two months later, saying her did it out of concern for her mental wellbeing.
The worker told the HDC he had was aware he had failed to observe proper professional boundaries by forming a friendship and entering a relationship with the client.
The support service's code outlined that it was misconduct and included staff forming relationships with clients and failure to disclose a personal, financial or professional relationships with a client
In her decision, Deputy Health and Disability Commissioner Rose Wall said by having a sexual relationship with the woman concurrently with a professional relationship, the man had breached the ethical standards and the standards required by his employer.
Wall said regardless of whether the relationship was consensual, the man failed to maintain appropriate boundaries and the relationship was likely to involve a "power imbalance and degree of vulnerability of the part of the service user".
The organisation providing the support service was not found in breach of the code because it had a code of conduct in place and provided training on professional boundaries.
The HDC recommended that support service use this case for wider education of its support workers. It was also recommended that the support worker undertake training in professional boundaries if he did choose to return to practice.