I'm not sure what's going on with it now, but I did used to read a comic called 'Grey is..." back in the day, before they left Smackjeeves due to what I think was fans trying to bully the creators into making their main characters a couple. But take that with a grain of salt, the reason could have been anything.
It wasn't too bad when I read it, it's got good art, and despite the comic being platonic there is a bit of a bromance vibe to it. But the authors did emphasis that it was a comic about friendship.
Other than that, I can only think of my fairly young melodrama, 'VTGtaHR'. Which, despite the title and main character being gay, is completely platonic. 100% just about people being good friends, and learning to live with themselves. Not going to lie, it's going to feature some uncomfortable subjects, and will be over-the-top dramatic for a while once the project kicks off. If you get uncomfortable by anything mentioned in the comic's disclaimer, you might not want to read it.