I know, I totally agree with you! I mean it’s just horrible how Asahi’s ex could say that to him. If I were her I be like, “And? I‘d still love you, and there’s always adoption” It’s like people forget that you can still love your foster kids as much as your own real child.
What I've gathered from reading manga, seems like adoption is never a popular option. I wonder if it's a culture thing for them. There are only a couple of popular adoption scenarios I've seen in mangas (yaoi and other genre):
1. Adopt a relative
2. Adopt child of someone they know/owe great favor to
3. Adopt a random child they pick off the street/alley
4. Actually being childless from infertility, but this adoption is usually not met with happiness in manga
Again, maybe it's a culture thing for them. I rarely read a manga where normal adoption leads to happiness.
Poor Asahi. He's been traumatized, seeing his "defect" reflected in memories about his dad. I like how realistic this manga portrays his struggle. It seems like originally Asahi really wanted to have a happy family, and children, to make up for the childhood he did not have. On top of finding out he couldn't, his ex also cheated on him, had a baby with another man, and said to his face "It's not like you can anyways, right?" That's traumatizing, to have your whole manhood and dream crushed in one go like that.
I don't think Asahi is having doubts about his relationship with Masato. The nightmare brought back haunting words from the past, suggesting that it's best if he settles for a man because he won't disappoint his partner with his "defect". First of all, that's a fucking horrible thing to say, to anyone, man or woman, because infertility is real and no one should feel like they're broken just because they cannot produce offspring. Asahi will eventually confirms that he's genuinely in love with Masato as a person, not because it's a gay relationship where he won't be judged for his flaw.