I think Kei's unemployment definitely also played a big role in his insecurities, but maybe because I share(d) the same type of "partner insecurity" as Kei, I still feel that Kei's bigger issue revolved around his love for, and insecurities with, Megumu. Not to say your points are not valid, rather, my personal experiences have skewed and influenced my opinion. The bottom line is as you said, however. Kei's cheating only served to (initially) push Megumu further away by projecting Kei's own insecurities onto Megumu.
In the case of the "Natsuki situation", personally I would have had the same reaction you would have. "Seriously? You're going to chase after my attacker without first checking on my well being? Dick!" I'd come unglued over that shit. Kei would have found himself and Natsuki in a bloody heap at the bottom of a very long flight of stairs themselves. My opinions on Kei's motivations were my attempt at objectivity and based only on Kei's conversations with their friend. As for why Kei chose Natsuki as a partner, my theory is that Kei wasn't aware that Natsuki would become so attached or violent. (I don't remember reading that Kei was aware of Natsuki's feelings, I could have missed that part.) My personal experiences, again, sway my opinion on this. There are times when a "temporary" partner will agree to the "no strings" idea at first, then suddenly become possessive and jealous, even stalker-like or violent. They seem okay... until they're not. By then, it's too late and you, or your partner, end up at the bottom of the stairs. This is why relationships like Kei's and Natsuki's are unappealing and troublesome to me. They just aren't worth the hassle. ╮(￣▽￣)╭
As always, our discussions are fun, thought provoking and enjoyable. I really look forward to them and enjoy every second. Thank you so much. (⌒▽⌒)
I'm one of the one that hates cheaters, but for this particular story, it was the outcome I think that upset readers the most (come on, seme left the uke after he was pushed down the stairs, to chase after the one he had an affair with, and the uke forgives him?). A satisfying ending to a plot like this, is where the uke grows a spine and leaves the cheater (because we all know that the likelihood of him cheating again is pretty high), then finds a handsome and sincere seme to ease his pain and fall in love with. Honestly, I think readers just wanted some justice.
To those who hate cheaters: WE GET IT. You all do realize this is a work of fiction, right? Cheating is a plot device for conflict. Without conflict, there is NO STORY TO TELL. Think about how many relationship conflicts there can be between two men. Now, how many of those make a good story? Exactly, not many. This is why you see so many stories with the same plot conflicts. If this bothers you, I have two suggestions - read something else or come up with a "never before seen" plot conflict. You may even become famous if you choose the second option and succeed. Good Luck.