"Shanna's moved on from Travis, but it's been hurtful that everything he's doing for Kourtney he did before for her, like the plane flying overhead, the flowers. It's all exactly the same," a source close to Moakler, who is dating Matthew Rondeau, tells PEOPLE.
Listen below to the episode of our daily podcast PEOPLE Every Day for more on Shanna Moakler's reaction to Travis Barker and Kourtney Kardashian's romance.
To celebrate the Keeping Up with the Kardashians star's birthday over the weekend, the Blink-182 musician took Kardashian for a getaway to Laguna Beach, California. While on the trip, he spoiled the Poosh founder with an airplane sky banner that flew across the beach reading, "Happy Birthday Kourtney."
The singer also gifted Kardashian, 42, with a massive floral arrangement in her home, which she showed off on Instagram.
While the source notes that "Shanna and Travis are cordial with each other and are friendly — they have a long history together," seeing his over-the-top professions of love for Kardashian — which are similar to what he did for Moakler, 46 — has been difficult for his ex.
"Again she's moved on from Travis and has her own boyfriend and life, but this is just hurtful to her," says the source of Moakler, who was married to Barker from 2004 to 2008.
Jeff Kravitz/FilmMagic Shanna Moakler and Travis Barker
Additionally, the former Miss USA is conflicted about Kardashian's relationship with the children Moakler shares with Barker. (Barker is dad to daughter Alabama Luella, 15, son Landon Asher, 17, and stepdaughter Atiana De la Hoya, 22, with Moakler.)
"Shanna of course wants her children to get along with their father's girlfriend," says the source, but when it comes to Kardashian buying the kids lavish gifts, "she feels uncomfortable. Shanna isn't as rich and can't compete with that."
Travis Barker/Instagram Travis Barker and Kourtney Kardashian
Since going public with their relationship, the pair have posted about each other on social media.
"Scott was pretty shocked when he found out that they are dating, and he can tell that they have moved very quickly," the source said about Disick, who shares Mason, 11, Penelope, 8, and Reign, 6, with Kardashian. "His kids love Travis, which is also hard for Scott. Kourtney and Travis are like a family with the kids. Scott is having a hard time with this situation."