Kelly Bensimon found out the man she’s been dating was locking lips with someone else just an hour before she walked the runway in a bikini for Miami Swim Week.

A source tells us that the former “Real Housewives of New York” star was backstage at designer Melissa Odabash’s show, “sitting in hair and makeup and she got a text,” that the man she has been dating, financier Robert Flood, was allegedly locking lips with his former fiancée at a bar in Westchester, NY.

A spy tells us that, “people were saying to her, ‘Don’t let this psych you out,’” before she strutted the catwalk in a two-piece suit to open the show last weekend.

We hear that Bensimon confronted Flood — who also briefly dated Tiger Wood’s former mistress Rachel Uchitel — a few days later,and is now trying to figure out what to do.

“She really likes him,” said a source. “It’s early, but that’s the last thing you want to know.”

We hear the reality star-turned-power real estate broker “is sad and trying to find a way to forgive him. But she’s also 57 and doesn’t want to waste her time. She doesn’t know what to do.”

Bensimon was photographed looking cozy with the Greenwich, Conn., financier outside Beefbar in Tribeca last month.

We have attempted to reach out to Flood for comment.

It was the first time the power broker was seen on a romantic outing since calling off her wedding to Scott Litner.  She also has a new iHeart podcast, “I Do, Part 2.”

Bensimon did not respond to request for comment, but did speak with us last week about her trip down the runway.

The model has been busy toning up for the job by seeing longevity specialist Dr. Amanda Khan for a regimen of peptides, we hear.

Dr. Khan has become the “it” doctor for New York’s social set, the Post previously reported, counting actress Jenny Mollen and reality star-turned-wellness whiz Lo Bosworth as clients.

Bensimon has been on the trendy NAD+ treatment, which purports to give cells energy.

“It’s a coenzyme that keeps the powerhouse of your cells working optimally,” Dr. Khan told us. “It’s creating the energy your cells need.” 

Bensimon also took glutathione, an antioxidant produced naturally by the body that drops with age.

“A lot of longevity medicine is replacing molecules you have lost by 40 or 50 to give you energy you had as a young person,” Khan told us. “That also reflects in your ability to exercise and recover from exercise.” 

Bensimon told Page Six, “It’s transformative. It changed my body.”

She listed off a slew of benefits she credits to the peptides she started taking in March.

“You feel healthier. Your skin texture changes, your hair and nail growth changes,” Bensimon told us. “It changed my entire body. I had bad gut health…  I have noticed a massive massive change.”

She also tells us, “My skin texture looks totally different. Tighter, brighter. People are like, wow you look so youthful.”

 The cost is $1,500 a month or $800 for a single visit to Dr. Khan.

Bensimon also says she ate “tons of protein and veggies,” and worked out with Equinox trainer João Martins.