The model and tennis coach said Miss Flack is loyal and kind, and criticised the "witch hunt" following the alleged row at her home in north London in the early hours of Thursday.
"I'm tired of the lies and abuse aimed at my girlfriend," Mr Burton wrote on Instagram.
"This is not a witch hunt this is someone's life. Caroline is the most lovely girl. Loyal and kind. She doesn't deserve any of this."
He denied he had signed a non-disclosure agreement, writing: "I have not signed any NDA. Why would I?"
Flack and Burton at Sexy Fish restaurant in Mayfair on October 16, 2019 in London. Photo / Getty Images
After Miss Flack was charged on Friday, her former fiance Andrew Brady, 29, posted pictures online of a confidentiality agreement he claims was signed during their relationship.
Mr Burton's post comes two days after he posted a selfie with the Love Island presenter on Instagram, decorated with a red love heart.
Police were called to Miss Flack's flat in Islington at around 5am on Thursday after reports that a man had been assaulted. Photographs of Miss Flack's front door showed what appeared to be blood stains.
Witnesses said that as Mr Burton was led from the property he shouted: "Bruv, I was normal until I met her."
According to The Sun, the incident was said to have been sparked when Miss Flack found messages from a 60-year-old woman - believed to be one of Mr Burton's tennis clients - on his mobile phone.
A spokesman for the TV star told the Daily Mail: "We confirm that police attended Caroline's home following a private domestic incident.
"She is co-operating with the appropriate people to resolve matters. We will not be making any further comment for legal reasons."
Miss Flack was bailed on condition she does not contact Mr Burton and will appear at Highbury Corner Magistrates' Court on December 23.
The hearing could prove problematic for ITV bosses as Miss Flack was expected to fly out to South Africa at the beginning of next month to front Winter Love Island. They are said to have held crisis talks.
Mr Brady, a former Celebrity Big Brother contestant, reacted to the news of Miss Flack's arrest on Twitter, writing: "Sad that I'm not more surprised by the news."
He later posted a picture of what appeared to be a non-disclosure agreement from March 2018 - one month before they announced their engagement - alongside the cryptic caption "#abusehasnogender".
Miss Flack's spokesman said: "Any suggestion Mr Brady has made that our client is in any way abusive would be false and defamatory."
The pair dated on and off throughout last year. Brady later moved to Australia, describing their relationship as "very toxic" and claiming that calling it quits "probably saved my life".
Miss Flack previously dated former One Direction singer Harry Styles, when he was 17 and she was 31. She said of the short-lived relationship: "It began to go wrong when he was pictured coming out of my house one morning. People started shouting 'paedophile' at me in the street and 'pervert'."
Miss Flack was then in a relationship with singer Sam Smith's manager Jack Street, but they split in 2014 just before she won Strictly Come Dancing. Between her relationships with Mr Brady and Mr Burton she briefly dated England rugby player Danny Cipriani.
The Metropolitan Police previously said in a statement about the alleged assault: "Caroline Flack of Islington was charged on Friday, December 13 with assault by beating.
"She will appear on bail at Highbury Corner Magistrates' Court on Monday, December 23. This follows an incident at approximately 05.25hrs on Thursday, December 12 after reports of a man assaulted."
Police confirmed that Mr Burton was not seriously injured. Ambulance staff said they treated two people at the property, which is currently on the market for $2.1million, with one taken to hospital.
