Joseph Manyang has also given evidence that despite pressure for him to reconcile with his wife, his relationship with his girlfriend, Akon Guode, 36, was stable and she had not threatened him or their children.

He continues to visit Ms Guode while she's in remand accused of murdering three of their children, and said she'd told him she felt dizzy when she was driving that day.

The pair's three youngest children, 16-month-old Bol and four-year-old twins Madit and Hanger died when Ms Guode drove her car into Lake Gladman, in Wyndham Vale in Melbourne's west, on April 8, 2015.

Their six-year-old sister Aluel was also in the car but survived and Ms Guode has been charged with attempted murder over her ordeal.

"She was a loving mother, she loved her children," Mr Manyang said at Ms Guode's committal hearing on Tuesday.

"We were good. We loved each other, we loved the kids."

When he fathered Ms Guode's younger children - the first born in 2009 - Mr Manyang was married to another woman, who also gave evidence on Tuesday.

The woman is still Mr Manyang's wife although the pair have not lived together since she discovered his relationship with Ms Guode in 2010, the court heard.

The woman denied allegations earlier made in court by Ms Guode's eldest daughter that she had threatened and verbally abused Ms Guode for stealing her husband.

In the months before the tragedy Mr Manyang, who did not live with either woman, had been visiting Ms Guode and their children about once a week, he said, and the last time he saw them was two days before the deaths.

The postal worker detailed that final visit in a statement to police, stating: "I did not notice any problems at the house, I played with the kids and then we talked. I don't recall anything was bothering Akon and don't recall any of the kids being sick or anything wrong as they were happy."

Mr Manyang said the couple had also spoken on the phone the day before the incident, about Ms Guode's planned move to Morwell to live near her aunt.

He missed a call from her about 2.18pm, less than two hours before she entered the lake about 3.40pm, but she did not leave a message, he said.

When asked if he was aware that Ms Guode owed thousands of dollars when she drove into the lake, Mr Manyang said he did not know about any financial problems.

He said when he asked her what had happened at the lake she would break down in tears and say she was "dizzy". "I'm still believing Akon, that she didn't do it," Mr Manyang told the court.

In his statement, he wrote: "Akon did not describe the accident to me. I asked her and she began to cry. She did tell me she got dizzy and I took this to mean dizziness somehow was involved in how the accident happened."

Before the incident, she'd told him she was taking medication for high blood pressure, he said.

Relatives of Ms Guode previously told the court she complained of headaches and dizziness in the months after the birth of her youngest child Bol, in December 2013.

Mr Manyang said police had asked him about rumours within the Sudanese community that he was separating from Akon. "I can say that I am not separating from Akon and there has been no discussion about doing this," he said in a statement last year.

But he added there had been community pressure for him to reconcile with his wife and that she was "now more agreeable to be flexible and is willing for us to get back together for the children."

The hearing continues.