Josh also alleged that Cathy had been "cold" towards him when the cameras weren't rolling.
"It's all good and well to act like the happy couple on camera, but it should be exactly the same off-camera too," he told the publication.
The couple's romance came to a head at Sunday night's commitment ceremony when Josh suggested they'd be better off as friends.
"I'm worried that we're going to be just friends next week, and that's all it is going to be. I don't want to be negative, but there's a difference between what you want and what you feel. I have doubts," Josh said.
She responded: "I actually walked into this commitment ceremony quite confident. I've tried not to think about too much of the future because it is quite overwhelming.
"But then I feel pressured to feel a romantic feeling in quite a short amount of time. You've given me an ultimatum by next week, and now I'm like, "Oh s**t'."