The 49-year-old interior designer began dating Clarke two years ago but made the decision to end the relationship because of his alleged betrayal.
The Mail On Sunday reports a friend as saying: "Everything came to a head when she started to suspect something was going on. There was a blazing row.
"Kelly gave Nicky an ultimatum but he continued to carry on with the woman Kelly was already suspicious of."
A spokesman for Hoppen confirmed the split but said his client had not ruled out a future reunion. "She feels the break will allow certain matters to hopefully be resolved," he said.