The 17-year-old star was dating student Julian Brooks - who is currently studying at the University of Nevada - who she met when they were at Sierra Canyon School together but was reportedly concerned he might have cheated on her.
A source told Star magazine: "He would disappear for days and not answer Kendall's text message".
She ended her relationship with the Julian as she "couldn't live with the doubt" after friends confirmed his infidelity.
The pair who are believed to have been dating for over a year were keeping their romance low key and were last spotted hanging out at the brunette beauty's father's beach house in Malibu, California, on the weekend of 4 July.
A source previously said: "They are each other's first loves."
Over that weekend Bruce Jenner - who is married to Kris Jenner -was surrounded by his family, teaching his girls, Kendall and Kylie, how to surf at the private beach behind his Broad Beach Bluff home in Malibu.
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