Why did they have to make this? The couple has already been through a lot. And it doesn't even make sense for there to suddenly be a son, who looks exactly like Iwaki and coincidentally is in love with Kato.
Shou is not in love with Katou (at the most he has a crush), and Iwaki is a bit jealous and hurt (more for the fact Shou deliberately provoked him throwing on his face his attraction for Katou). It's totally understandable. Iwaki is older than Katou and probably unconsciously he fears Katou might leave him or fall in love with someone younger.
I wouldn't say that Shou's in love with Kato, it's more like he's desperate for a father/son bond with Iwaki and the fact that his only link to his father is Kato makes it even worse. Especially when Iwaki has a better bond with Kato's nephew. Personally I think they're making a mountain out of a mole hill about revealing Shou and Iwaki's relationship, I think the public would understand that Iwaki didn't know he had a child until now and they'd probably applaud him for wanting to be in his son's now and working on their relationship since it's clear that Iwaki really wants to be a father and desperately wants to have a great father/son relationship with Shou, since his own relationship with his own father isn't good.
you're all amazing people for understanding Iwaki's feelings instead of hating on him (▰˘◡˘▰)
I already guessed what the seme meant, when he talked about the present. But I almost felt bad about continuing, since the uke truly believed in him and was so happy about it.
I hate those parents for being so selfish and irresponsible. They should at least make sure that their own child get the care he needs before going out to help other children.