The man, aged 21, pleaded guilty to inflicting grievous bodily harm on his partner.
When he appeared before court, he also admitted to using threatening words towards his girlfriend six days after the assault.
He was given six months in jail, suspended for two years, with a further one day’s prison, also suspended, for the public order offence.
It was a month after the couple had split up that the pair bumped into eachother at Joanna’s Disco, Southsea, said Nicholas Atkinson, prosecuting.
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It was on this night that the man proceeded to headbutt his would-be fiance’s nose, twice, also dragging her into a side street and slapping her.