he gets beaten up by his biological father, his best friend chooses TX over him, and his family gives up on him. Additionally, although he is ill and needs professional medical attention, it seems that his family lets his (possibly abusive) biological dad force him to live in the countryside where that help may not be as readily accessible (which is one of the reasons why his biological mother swapped him at birth). YD hates his biological family, as well as his new environment.

then, in this chapter, MC and ML intend to have dinner together, MC considers it a date. but ML couldn't come because Yang Doule (child who switched with mc) was sick. I think MC should give up (although I know he's hurt, but you can't fight over ML to leave sick people right?)

first, if ML doesn't read MC's letter and doesn't like it, isn't MC live in the shadow of 'other's child'?

second, if MC is not switched, he lives with his rich family and grows up with ML, but MC will still like ML but will ML still like him too? (I don't think so, even if ML says it in the novel, I still have doubts, even the MC himself has doubts. You will know after much reading.)

Third, let's look at it from the point of view of Canon Fodder, Yang Doule. I actually read too many novels from canon fodder's point of view, and it made me feel sorry for Yang Doule. say, he did not ask his mother to change his fate to become a rich child. however, he had lived so comfortably, so, YD's hostile response to the MC seemed human. I mean, who doesn't want to live comfortably? YD must have thought that after his fake family found out that MC was their real son, YD was afraid that he would be forgotten and thrown away.

Fifth, in the end ML's mother did not make amends to ML at all.

then because the guiltiness she jump off the building, well she had already had illness which need kidney transplant

At first he was very indifference toward MC. But he protect MC pretty well later on, like to tease MC from time to time.