Smart move. This has been translated into English for almost 2 years now on otakumole and after chapter 41 it becomes such a convoluted (and I should say psychotic) mess that you'd end up wondering what kinda drugs the mangaka was taking to turn what began as a pretty normal romance into such a twisted, overly dramatic sh*t storm.
Well, I'll try to hide this in a SPOILER in case anyone doesn't want to know...
The story gets very stupid and rage inducing after chapter 41. The idiot girl loses her memories while still in a relationship with the younger one. He is moving away so he doesn't tell her that she's his girlfriend. The black-haired dirtbag 3rd wheel takes advantage of her (in more ways than one) and she ends up going out with him and eventually falls in love with him. It gets really messy from then on involving another 3rd wheel, a forced lover's suicide attempt, etc, etc, but eventually the younger one returns just in time to save her from committing suicide whence she suddenly recovers her memories and they become a couple again. The End.
My advice is that you all pretend that this is the final chapter and ignore any further chapters you may encounter. The main couple is together for now, and the dirtbag 3rd wheel seems to be out of the picture, so do yourself a favor and mentally mark this as complete. If you actually ever read all the way to the end (another 43 chapters), there's a 99.99% probability that you'll say to yourself, "WTF did I just waste my time reading?" and, more importantly, "WHY?"