Mendes, 23, said in an On Air with Ryan Seacrest interview Tuesday that he and the "Don't Go Yet" singer, 25, are in a good place months after their November breakup.
"[We're] so friendly. I mean, I loved Camila first for so many years and that's never gonna change," he said.
The singer told Seacrest that his new song "When You're Gone" — which features revealing lyrics about trying to get over a difficult breakup — was written about a month after their split, and he found the writing process healing.
"I think it's really just the processing and the complexities of that, the complexities of knowing something is better and still wanting to hold on and all the reasons why," he explained. "I'm really glad to be able to just be real and authentic with my music because it's cathartic for me too, to be able to write about these things."
Jeff Kravitz/FilmMagic Shawn Mendes and Camila Cabello
Mendes also told Seacrest he related to the feeling that happy relationships can sometimes be scary, as there's always a lingering fear that they'll end and the aftermath will be too difficult to handle.
"I think most people have that fear, but in a lot of ways, I think a breakup can be a blessing too, because it can really show you that you are [strong enough], which is necessary," he said.
The star previously said that he ran the lyrics of "When You're Gone" — which includes lines like "I didn't know that loving you was the happiest I've ever been/So I'm just tryna hold on" — past Cabello before releasing the song.
"Camila and I have always been writers for as long as we've known each other, so we understand what that means," he told Extra. "And we respect what that means. And there'll always be transparency between us."
The "Señorita" singers announced their split in November after two years of dating, saying in a statement at the time that they would "continue to be best friends."
Cabello, for her part, has also dealt with her feelings through song, and alluded to the split in the lyrics of "Bam Bam," her single with Ed Sheeran.
"We were kids at the start/I guess we're grown-ups now/Couldn't ever imagine even having doubts/But not everything works out," she sings.