A man accused of causing or allowing the death of a three-week-old baby celebrated the birth with a "cocaine baby shower", a court has heard.
Sam Davies, 24, from Gosport, told jurors he had "never been happier" than when the boy was born in March 2017.
Stanley Davis died in hospital from a skull fracture 24 days later.
His mother Roxanne Davis, 30, and Mr Davies, her then partner but not the baby's father, have both denied causing or allowing the death of a child.
Stanley had already suffered 41 fractures to his ribs, arms and legs by the time of the fatal head injury, Winchester Crown Court has previously heard.
Giving evidence, Mr Davies said he did not cause any of the injuries or allow the baby's death.
He said he was "over the moon" when Ms Davis, of Lee Road, Gosport, told him on their second date that she was already pregnant by another man.
"It gave me what I've never had, a proper family," he told the jury.
Mr Davies said he held a "mini baby shower" on the night of the birth, taking cocaine with Ms Davis' brother.
He told the court the couple's relationship later deteriorated, to the point where she punched him, spat in his face and smashed ornaments at their flat at Garland Court in Forton Road, Gosport.
Mr Davies, now of Mayfield Road, Southampton, said he had "booted a mirror" and sometimes "punched walls" to calm down.
The court heard Mr Davies had been diagnosed as having behavioural issues including ADHD and used cannabis daily in order to function.
Mr Davies said Stanley was "passed around like a parcel" by his former partner's friends, which may have caused a bruise which was later noticed by a health visitor.
He said the baby had been unwell for three or four days before being taken to hospital on 21 March 2017.
Stanley had been making "weird" hand movements, he said, and his eyes were staring and watery.
A few hours before the final hospital visit, Mr Davies said he grabbed his partner during an argument and she fell with Stanley in her arms.
"She remained upright. Stanley was fine," he told the jury.
Later that evening he became concerned that Stanley was "twitching" and said they should seek medical help.
Ms Davis posted a video of him on Facebook, asking for advice from friends, he said.
The jury was also told of a previous incident on 8 March when Mr Davies awoke to find his partner loudly mimicking the baby's crying.
"Her arms were going up and down with Stanley. I said, 'What's going on?' She said, 'He's grouchy. Mind your own business.'"
The skull fracture, which led to a fatal brain haemorrhage, probably occurred 16 days after Stanley's birth, the court has heard.
Previously prosecutors told the court that one of the couple killed the baby while the other allowed it to happen, although they could not say who played what role.
The trial continues.