"Christian is an easygoing guy, the kind of guy that was never bothered by the mass attention Gaga got while they were together," the source notes. "He didn't go to Instagram for attention or for revenge. Christian was on the set of A Star Is Born and so was Irina. They all became friends."
"Christian and Irina have a lot in common, they both feel they lost love because of their partners' endless work and dedication to their careers," the source continues. "Christian liking Irina’s Instagram photo is just his way of being supportive of her."
The source says that 44-year-old Cooper and 33-year-old Shayk grew apart due to the actor being more focused on supporting A Star Is Born -- which he also directed -- and her being more involved with their 2-year-old daughter, Lea De Seine.
"After the movie was complete, Bradley became very involved in the promotion of the film, while Irina became very involved with the baby. They argued a great deal, and it affected their home life," the source says. "Their relationship didn't work out because Irina was looking for more of a family life."
However, the source says the exes are working things out so they can successfully co-parent.
"Irina is focusing on her child and holding herself together after a painful separation," the source says. "They are working on custody arrangements and want to make sure they work things out so they can co-parent."
"Things were difficult before Bradley started filming A Star Is Born, but his dedication to his work while making the movie only made things harder at home," the source said. "The constant speculation about Bradley's relationship with Gaga -- while things were difficult at home -- didn't help the situation. But his relationship with Gaga is not the issue. They have many daily issues as parents and as professionals and have been fighting."
"Their troubles have been going on for quite some time and they even considered splitting during the release of the movie," the source continued. "They talked things through a great deal and seemed to hold off and keep up appearances for the time being. It was recommended they delay a split at what seemed to be the peak of his career because the negative attention would take away from the excitement of the release."