The background as to hy Hyesung felt he had to drop out of education, left home and was disowned by his dad was far better explained and more realistic than in this series where Hyesung apparently did all of the above, but simply because he couldn't pass his math exams. In " If you hate me so much", Hyesung's dad walks in on him having sex with another man, kicks him out and beats him to a pulp. If the author portrays the dad as some harmless "tiger parent" who just wants his kid to get no. 1 test results, it will be very odd.
Well... A dad walking in on his son having sex with another man is already traumatic for the dad. I feel bad for him but kicking his son out and beating him to a pulp is already pretty harsh tho but I think it was just impulsive for his dad I guess. After all, I've never met a parent who doesn't love their own child, I don't know about adopted children tho.
This manga is a official doujinishi of the manga "if you hate me so much". The main characters of this manga are the same characters(hyesung and dojin) from if you hate me so much but in very different settings. This manga is a omegaverse in which dojin is an alpha and hyesung is an omega.
Hope this explains the question.
Doujinishi or dj is the type of manga where you take characters(appearance and name) from one manga and make a entirely new manga having different storyline and concept etc. For ex you would see a lot of dj of popular manga such as free, attack on the titans(which are not yaoi mangas) but most of them are made into you.(most of the dj are made by fans and amataur artists).
I said it is a official dj cause the same mangaka has written the dj as well.
It's really funny and cute how in "If You Hate Me That Much" they are all normal people in normal world but in "Love Is An Illusion" they are all in omegaverse (≧∀≦)