The former glamour model was photographed on a night out with the boxer and supported him during a recent fight in Los Angeles. The Sun claims that Reid knew he was fighting a 'losing battle' to save their relationship.
"He feels blown apart," a friend told the paper. "The breaking point for Alex came when he saw stories about Katie and Amir Khan.
"Then when Katie announced she was running the London Marathon with Andrew Gould this year, it was another nail in the coffin."
They added: "He just feels blown apart but is also really angry. He feels he is being used as some emotional experiment."
Reports have suggested that the couple will announce that they are to split up this week, following Price's apparent confirmation that their marriage is in "crisis".
The paper also claims that Price was overheard declaring that it was "two down, one to go" at a party over the weekend.
"We asked Katie if it was true she was getting a divorce," a guest at the event said. "She was completely blasé about it and just said she was looking forward to the third husband, as long as he could give her another child. It was a cynical and cruel thing to say."
> Katie Price 'keeping Reid hanging on'