Today the male teacher's partner gave tearful evidence at the tribunal.
At the time she was suffering from severe ill-health that she said affected her judgment.
She first met the girl when, drenched and cold, she turned up at the teachers' house one night in a storm. She didn't want to go home and, reluctantly, the teacher let her stay.
The male teacher wanted to tell the school principal but the girl "begged" him not to, the female teacher said.
She was not comfortable about letting the girl stay but later agreed with the male teacher the girl could be there, if she had nowhere else to go.
But the male teacher initially didn't tell the female teacher the girl was self-harming, or about the extent to of the communication.
The girl later went to boarding school but returned home after more self-harming and a suicide attempt, the female teacher said.
She and the male teacher would visit the girl in hospital, but were asked to take a step back until once night they helped look for her when she ran away.
That night they found the girl - "the most distraught person I have ever seen in my life" - who was adamant she didn't want to go home. She didn't say why.
"[The male teacher's] relationship with [the girl] was one of mutual respect," the female teacher said.
"They had a good rapport and they had a lot in common. [The male teacher's] an incredibly loyal person and he has a huge heart.
"When [the girl] first asked [the male teacher] for his support, I believe he responded as best he could. He got dragged further into the relationship when [the girl] turned up at our house."
The female teacher said her partner's relationship with the girl became one of friendship. It was not intimate, but it was unprofessional.
The female teacher had since read the exchanges between her partner and the girl.
"It was difficult for me to go through and I understand how it reads. At times [the male teacher] used language that is unprofessional. He uses a lot of effusive language he used when he is speaking and that translates very differently when read or when people haven't spent a lot of time with him," the female teacher said.
"I'm very aware it's not OK for a student to stay at a teacher's house. In the end we chose to look out for [the girl's] immediate safety by putting a roof over her head. It was not the [male teacher's] or my responsibility to take [the girl] on. If we had told the school on the first night she showed up we wouldn't be in this situation now."
The male teacher admits a serious misconduct charge but disputes some of the allegations against him. His partner admits wrongdoing but says it doesn't amount to serious misconduct.
The names of the teachers, the girl, the schools involved and where this happened are suppressed.
The hearing continues.