I agree to an extent, they never did pay for the damages to his car. And all four of them are in a similar situation so it would have been nice if they were more courteous. But I do understand their need to be cautious and a bit weary as it is that kind of uncertain situation. They are acting sad probably for the reasons the previous commenter (Kiyotake) has stated. And I will add that yes they should learn to be more like Bexan and Minsuk and learn to appreciate what they have with each other.
You can't embrace a wolf the same as a human. It's sort of sad that they can't enjoy themselves--go on dates and do daytime things as a human couple. Plus, we don't know enough about Ein and Diesel to make a conclusion about their behaviors. Sure, they are both dicks for not fixing Minsuk's mini cooper especially since Ein is driving an audi! They've probably been together much longer than Bexan and Minsuk and have experienced hardships that made them so cold acting. Sp, we'll be learning about them. Hopefully, Diesel won't come inbetween Bexan and Minsuk. Plus, Diesel is from Germany so how did he end up in Germany and how did Bexan end up in S. Korea if their kind is in Siberia aka. Russia?
I really like the second couple. A cool, mature older man and a long haired protective beauty. Honestly, I'm not that mad at Diesel for hitting Bexan. I just assumed that they're ruled by their animal sides when it comes to strong emotions like anger and love. And it's not that difficult to imagine why they're so sad when the sun rises. They appear to have been with one another longer than Bexan and Minsuk. Bexan and Minsuk are barely in the beginning of their relationship. Diesel and Ein know how lonesome it is to be next to each other but not truly be "together." I feel they must've gone through really troubling times together
I don't like the background couple at all. Acting like assholes and all high and mighty. Also, what's so sad about Diesel turning into a wolf? The wolf is part of him. Look at Minsuk. He cuddles the dog and bangs the human. Perfectly fine to like both.
I love how Minsuk and Besan look here and I love how comfy they're around each other, regardless of Besan's current form: http://www.mangago.zone/read-manga/wolf_in_the_house/nmt/c016/47/