Kelly, 33, is said to have thrown 25-year-old Danny out of her London home after discovering he had been seeing a string of other women behind her back.
In April, Kelly nursed Danny back to health after he was knocked over by a bus on a drunken night out, however a newspaper has claimed he was two-timing her even then.
Yesterday, Kelly cryptically tweeted: "I often wonder if more girls were willing to be ladies, would more guys feel challenged to be gentlemen." She has since deleted the tweet and all pictures of Danny.
According to The Sun, Danny has confessed to a pal that he cheated on Kelly - who he rekindled his relationship with earlier this year.
"He just can't believe what he's done - he just wants Kelly back," Danny reportedly said.
Meanwhile, Instagram user Stacey Simcox has told the newspaper that Danny got in touch with her on the social networking site and began sending her saucy messages.
She claimed: "He'd send me filthy messages about what he wanted to do to me and begging me to meet up for sex."
Reveal has contacted Kelly's rep for a comment. Danny's rep told us: "Nothing more is being said at this time."
Danny and Kelly first began dating in 2008, but the couple split in 2010. Kelly then went on to date fellow rugby player Thom Evans, however their relationship fizzled out in February this year.
Weeks later, Kelly and Danny were spotted out together. This sparked rumours that they had reunited, although to begin with the couple kept tight-lipped.
But when Danny had his accident, Kelly - who was starring on ITV2's Celebrity Juice at the time - made no secret of their relationship and rushed to her boyfriend's aid.
She also told fans that she was a "loving nurse" who had been making him chicken soup.