No, no. I think most people got that Sangwoo never actually used his dick on Bum. But a lot of people, including me, were really confused about Sangwoo’s motivations throughout this whole scene. I think a lot of us (wrongly) thought Sangwoo was trying to hurt Bum, when in fact he was doing his usual thing of trying to be a good boyfriend and failing miserably.
I think the reason we got confused is because we assumed Sangwoo would be pleased after Bum killed Jieun. It was a huge shock to the system when Sangwoo got angry and threw a bitchfest and tried to throw Bum out of the house for not appreciating his gift.
I didn’t realize, until I re-read the chapter, that by the time Sangwoo picks up the dildo, he’s not mad at Bum anymore. Bum refusing to leave and running back into the house probably reassured him a bit. So, bizarre as it may sound, Sangwoo raping Bum is his way of trying to calm him down and make him feel better. He genuinely believes Bum’s cries to stop are just an act, because he believes Bum has a rape fantasy (and he’s probably not entirely wrong.)
I don’t think Sangwoo is getting sexual gratification out of the situation, at least not at first. He probably gets into it more later when Bum starts saying romantic stuff about wanting to be with him forever. But before that, Sangwoo isn’t doing this for fun. He’s doing it out of obligation to his new husband.
As for whether Bum wanted it…it’s hard to say. I think he got off on some parts of it, but he’s out of his mind right now and doesn’t really know what he wants. I think after he finds out Sangwoo is using a dildo, he stops enjoying himself.