
Clothes comes from the store that belonged to his mother. After she died she left it to He Yang and the person who runs it in his stead sends him the clotes everytime they release something new, so he just gives them to Yang Yang. That stupid fucker Shen buys the clothes from the store with his own money. So Yang Yang really is not a stand-in its just He Yang is a terrible boyfriend and an emotionally constipated.

If I recall correctly, ge does so because Yan Yan was looking at him so 'intensely' and 'lovingly' that He Yang felt guilty he couldn't love him back like he deserved (he wasn't aware he was already in love with him) so he blindfolded him to avoid his gaze. And he does him from behind because he just likes the position? Yan Yan's ass is too sexy to resist I guess. There is no speacial meaning or explanation for that one he just likes doing it that way.
It's been so long since I read this manhua and even longer since I've read the novel so my memory is a bit fuzzy but he should explain these in the chapter where he gives him the apartment back and Yan Yan lashes out at him after seeing the closet.
Wait how is he trying to pull off that he wasnt a stand in now after dressing him the same? What was his excuse for that?