The news comes shortly after photos of Younes getting cozy with another woman, former Las Vegas waitress Jordan Ozuna, in Mexico on Monday surfaced on TMZ.
But Younes reportedly denied any wrongdoing on his part, writing in an Instagram story, "They really want me to be the bad guy. F-ck your Hollywood bullsh-t, can't have fun with your friends no more."
Despite taking a romantic European vacation together last month, breakup rumors began to swirl when Younes appeared to criticize Kourtney on social media when she posted a photo of herself in a floral thong from the three-week trip.
"That's what you need to show to get likes?" Younes asked in the comments section of Kourtney's Instagram photo, although the post has since been deleted.
"He never liked that she posted sexy pictures of herself on social media," said the People source.
"He doesn't want his girlfriend to do that. He gets that it's her job, but wants her to post more covered-up pictures. He has always had a problem with this. This is the stuff they argue about and what made them split in the past."
Kourtney and Younes reportedly met in Paris in October 2016. Younes, who is Algerian and speaks fluent French, acted as a translator for the reality TV star's family after Kim Kardashian was robbed at gunpoint.
The couple went public with their romance in May 2017, and things got more serious in subsequent months as they traveled to the south of France, Egypt and Paris. By December, an insider told People things were "definitely" serious between Kourtney and Younes.
"No one thought their relationship would last this long, but Kourtney is very happy," explained the insider at the time.
"Kourtney's family really likes him. He is the opposite of Scott. He doesn't party, isn't flashy and really treats Kourtney with a lot of respect. It's obvious that he really cares about her."
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Prior to getting involved, Younes reportedly dated model Jourdan Dunn, and Kourtney was wrapped up in an on-again, off-again relationship with the father of her three children, Scott Disick, for nearly a decade.