Though Rob, 27, flew into Florence, Italy, with the rest of the family to attend the nuptials, he flew home to Los Angeles before the couple exchanged vows.
"He sent me a long email the morning of that he was gonna leave and there was no fight," Kardashian, 33, revealed to Andy Cohen on Tuesday's "Watch What Happens Live."
"I just thought, 'You know what? This is my day. I'm not even gonna worry about it. I hope he's OK. I totally understand that he wouldn't want to see a lot of people if he was feeling uncomfortable,'" she said.
Kardashian added, "You can only pray and wish that someone would not miss out on more memories in life 'cause life's about memories. So, fix the problem. That's just how I am, but we didn't even have a conversation about it."
Earlier, Kardashian explained that she's a "tough love" type person who makes a change whenever she's unhappy with something and that she sometimes loses patience with her younger brother.
"I try to encourage him and once you don't make that change for so long, and it's not happening, I get frustrated. My patience runs out," she said.
She prefaced her words with, "My brother and I are so close. He's one of my best friends."
For his part, Rob recently posted a photo of Kardashian's 1-year-old daughter North West, his niece, gushing, "Goodness @KimKardashian she's soooooo pretty!!!! LOVE HERR."