Cape Town – Diego Novella told the Western Cape High Court on Monday that Gabriela Kabrins Alban was abusing unprescribed pharmaceuticals before her death.
Kabrins Alban was taking medication for Lyme disease after having been misdiagnosed with Addison's disease.
Prosecutor Mornay Julius cross-examined Novella about whether Kabrins Alban's medical condition affected their relationship after she moved in with him in Guatemala City in April 2014.
"Yes. She was misdiagnosed and was taking Hydrocortisone – the worst thing you can give to someone with Lyme disease – [that], coupled with unprescribed medicine, affected our relationship," said Novella.
Novella also told the court that he believed Kabrins Alban's daily routine contributed to the problems in their relationship.
Due to her medical condition, Kabrins Alban would sleep all day and wake up in the evening.
Sickness turned her 'into another person'
"At the beginning, I didn't know what I was dealing with," said Novella.
"I tried to soothe her as much as I could. Of course it affected our relationship."
Novella also told the court that Kabrins Alban's medical condition "converted her [into] another person".
"When she went back to Los Angeles in 2014 and her dad saw her – her dad said 'this is not my daughter'," Novella told the court.
Novella previously testified that he had defended himself against Kabrins Alban whom he believed to be a "demonic entity" at the time.
The Guatemalan has also admitted to throwing foodstuffs on her body before defecating on her.
He is on trial for murdering Kabrins Alban at a Camps Bay hotel on July 29, 2015.