The actress - who has daughters Sam, six, and Lola, five, with ex-husband Charlie Sheen - began dating the Motley Crue bassist late last year, but friends say they have decided to call time on their brief romance and insist it was never serious.
One pal told Us Weekly magazine: "It`s crazy how this is being made out to be some big break-up. They were never exclusive or serious to begin with! I could count on my hand how many times they went out. This isn`t some big, dramatic split."
When Denise, 39, and 52-year-old Nikki - whose real name is Frank Carlton Serafino Ferrana, Jr. and is a former heroin addict - were first linked, friends said they were taking things slowly.
One revealed: "They have been neighbours for years. They have a lot in common and are taking things slowly".
Before dating Nikki, Denise was single and previously revealed she finds it difficult to combine the needs of her children while having a personal life.
She said: "Dating is very challenging. I won`t introduce my kids to anyone I`m dating unless it`s very serious. And balancing everything - my daughters always come first. I will never get these years back with my girls!"