beta
Although I agree that the ML is a dirt bag, hope he gets abandoned for a long while, it's interesting that he does not actually reveal anything about his background to the MC. Not excusing the bastard, but the most he's personally revealed is that he does not have a good relationship with his father. Everything else has been told by his sister, which she's clearly using to try and manipulate the MC.
This either means that 1. The bastard is being somewhat honest in his approach to the MC, because he's trying to charm him into staying rather than just relying on his sad background. He's still a shady bastard nonetheless but he's not using his past to his advantage. 2. He told his sister to do it. I don't put it past him not gonna lie. I believe the bastard is trying to influence MC through outside means, but he's failing because nothing is really sticking long enough not to raise doubt. Interestingly, MC is even doubting the lab results, which I don't put past the bastard to manipulate either. The bastard IS using their son, so if it seems the treatment is going 100% well (not just 80% or 90%) then the MC is more inclined to stay.