To be quite honest, it'd be interesting if they didn't end up together.
Basically, I'm not very romantic. I believe there are many ways to find happiness. While I am not quite of the same opinion as Joyce, whose Molly Bloom basically says she could have ended up with anyone, I don't think there is just "the one" out there waiting for us. People can make it work, if both sides are willing to make concessions, listen to each other and become slightly different from the interaction with their spouse. I hold up as an example to be followed a couple I knew who, once they decided to live together, spent one whole year systematically talking about everything they considered important until they reached an understanding. And then went on to live 31 years together, until she died. It definitely wasn't the all-devouring fire of passion, but a tender, robust partnership they fueled daily. One of the most beautiful couples I've met in my life.
So this break up of the protags is realistic, it's painful, but right now, I see it much more as the pain of breaking any close relationship. It hurts, because everyone we hold dear leaves a gap in ourselves when they are no longer there.
They will overcome. And they're not doomed to misery. I'd love it if this story moved on to show them each hooked up with a new interest, re-educating their hearts, and then were able to meet each other and resume their old friendship in a different, less mutually-dependent but still intimate way. Sitting down in a café to talk about life, spending time at the phone/live chat, maybe double-couple meeting every now and then.
After all, this webtoon is titled "My male friend".