Long-time psychologist Vincent Cicconi was found guilty of professional misconduct and stripped of his registration for at least 15 months, in the Victorian Civil and Administrative Tribunal (VCAT).
The patient sought counselling from Cicconi in 2008 after breaking up with her long-term partner, according to a VCAT judgment.
She was abusing alcohol, ecstasy and marijuana, and Cicconi described her to Centrelink as "basically homeless" and "unable to look for work given her mental state".
But the pair began visiting restaurants, concerts and the cinema together while the woman was attending counselling sessions with Cicconi.
Soon after the woman stopped the sessions with Cicconi she became his lover, temporarily moving into his home.
The Australian Psychological Society's code of ethics states that psychologists cannot have sex with a former patient for two years after ending the professional relationship.
The pair's "erratic and tumultuous relationship" eventually turned abusive and Cicconi was charged with assaulting the woman.
VCAT deputy president Heather Lambrick and members John Farhall and Marian Power condemned Cicconi's relationship with the woman as a serious breach of trust.
"(The patient) was extremely vulnerable. She required dedicated professional assistance. She did not receive it," the tribunal said.
"When the patient is vulnerable and the health professional is being consulted to assist the person to address the subject matter of that vulnerability, the conduct becomes all the more serious a transgression."
The tribunal accepted that Cicconi was out of his depth dealing with a patient as complex as the woman, but said he should have referred her on to someone more qualified.
The tribunal also ruled that Cicconi misled the Psychology Board of Australia when he told them he did not have contact details for the woman.
Cicconi, who practised in Moonee Ponds in Melbourne's northwest, was deregistered and banned from reapplying for registration for 15 months.
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