I'm pretty sure the last one is still not consensual. He's been blackmailed/threatened and coerced. Coercion by sex is rape. With the guilt the uke experiences in beginning of season 2, it can be Stockholm syndrome and/or trauma (hence the name of the manga). Why uke may be coping with sex could be a coping mechanism for the sexual assault he went through.
like the person said, the novel is a lot more detailed than the manhwa. at this point in the story their relationship was a lot more.. tame(still not healthy) and the uke was beginning to trust the seme quite a lot, he initiated and wanted the sex, he wasn’t coerced into it and even after jeongin said stop he would pull seunghyun back in with his legs
In the novel, things are more clear because we know what the uke is feeling. But just so you know, what the seme and the uke are doing in the last chapter of season 1 is consensual. It doesn't matter if you think it's rape or not. It is not. But the uke got so scared that his family found out he is gay (they are trash) that he accused the seme of rape, even though his family know it's not true, but they are too uptight and don't want society to find out their son is gay.
And now the seme is back, after spending years in prison, to get revenge and the uke feels so guilty that he will let him do anything. The uke has been dealing with the guilt through s3x (letting men use him) and alcohol and he is like a dead person just going with the flow but not really living.
The novel is not translated as far as I know, you can only buy it on the same platform as the manhwa.