Things are going from bad to worse for baby-oil heiress Casey Johnson — she’s now been dumped for good by her close friend and ex-lover, Courtenay Semel.

Semel, the daughter of ex-Yahoo boss Terry, says her fiery, on-off relationship with the Johnson & Johnson heiress is finally over and told Page Six: “I wish her well — but well away from me.”

Semel, who was recently named Hollywood’s hottest lesbian, said she’s ditching Johnson after she was accused of breaking into the apartment of mutual pal Jasmine Lennard and stealing her clothes, shoes, jewelry and legal papers.

Semel told us, “I have suffered emotional torture and manipulation at the hands of this woman, and never before has she suffered consequences for her actions.

“This was a long coming. It’s time for me to have a life. The truth is that she needs to get serious help. But what worries me is that she will hit rock bottom before she does that.”

Semel added, “This thing with Jasmine — I really don’t want to be in the middle of it. It’s a nightmare. I promised to my family I would not get into any more trouble, and now I have to give statements to the police about Casey. I’ve had enough.”

The Post revealed last week that Johnson allegedly broke into stunning model Lennard’s Hollywood pad and ransacked her possessions, leaving a vibrator on the bed.

Johnson was busted when Semel texted Lennard, saying, “There’s a problem, Jaz, Casey Johnson just got into bed with me and she is wearing your underwear. There are documents here, your shoes and your clothing — you need to call the police.”

Johnson, who denies stealing Lennard’s possessions, faces a year in jail if convicted. She refused to comment on Semel’s remarks.