Quote from chineserider
No, it's not NG Boy x Paradise. This manga has a darker ambiance.
And yeah, BlackOrion, the ending threw me off a bit. The girl cheats on her boyfriend with his younger brother. I tried the tags and from my own lists but still couldn't find anything.
Well sorry to hear that, hope you find it (yeah it's kind of an odd ending , seems like i don't read enough Josei)