People: Scott Disick Struggles Seeing His Ex Kourtney Kardashian Move On with Travis Barker

Reality star Kourtney Kardashian and her musician beau Travis Barker are very happy with their new relationship, but the same cannot be said for Scott Disick.

A source close recently told People magazine that Disick is having a hard time with Kardashian's new relationship, adding that it was hard for him to accept she has moved on with Barker.

According to the insider, Disick has always been jealous of Kardashian's past romances but recognizes that her romance with Barker is different.

In the past, Kardashian's past relationships were always nothing more than flings, but things have become serious pretty fast with Barker. The source said:

"Scott was pretty shocked when he found out that they are dating, and he can tell that they have moved very quickly."

Moving quickly entails Barker meeting his and Kardashian's three children, Mason, Penelope, and Reign, all of whom have taken a liking to the musician since he started dating their mom.

Seeing his ex's new relationship flourish and grow so fast apparently makes Disick very uncomfortable because to him, Kardashian and Barker are like a family with the kids.

Barker penned a heartwarming birthday tribute dedicated to Kardashian.

The source noted that Disick regrets how his years-long relationship with Kardashian turned out, adding that he knows he messed things up and let her down in the end.

Kardashian and Disick ended their romance in 2015 after nine years together. They have, however, since maintained a cordial co-parenting relationship and have remained close friends.

According to the source, Disick hoped he and Kardashian would get back together for the longest time, but the new relationship with Barker makes it a bit far-fetched for now.

In a preview of Thursday's episode of "Keeping Up With the Kardashians," Disick told Kardashian he does not like seeing her with another guy and admitted to it being difficult for him.

Kardashian was first linked to Barker in January, and after making it Instagram official in February, the pair has constantly shown off their love for each other on social media.

Last weekend, Barker penned a heartwarming birthday tribute dedicated to Kardashian as she turned 42. He shared a series of adorable pictures alongside a sweet caption expressing his love for the reality star.

In addition to the tribute, Kardashian also received the sweetest birthday gift from her beau: a massive floral display that she proudly showed off on her social media.

Kardashian and Barker's relationship might only be a few months old, but these two are clearly in love and can't seem to get enough of each other.