I agree with you. Her reaction isn't surprising by today's still existing standards.
I think what hurts me the most is her thinking that it's HER fault. She thinks that her cheating has traumatized Taiichi into rejecting women and turning to men. It's sad that she misunderstood his genuine love for Naoto with a forced-trauma-induced love without hearing him out first. (/TДT)/
This story is hitting all the feels right now
"She thinks that her cheating has traumatized Taiichi into rejecting women and turning to men."
Exactly! And it's a very selfish way to evaluate the situation, think that she was the cause of her son's homosexuality and not because Naoto was the person who was there cheering him up and by his side in that difficult time showing him support. She's still after of this time thinking in her own feelings only, not caring about his son at all. I agree with your POV too!
Shit is getting real in this manga. But I don't exactly blame Taichi's mother for her reaction, it seems that today there's still some issues regarding with homosexuality and her reaction is pretty realistic. If there's something that it needs to be said about her is why she waited so long to reconnect with her son? and on top of that appearing with a daughter? (beautiful child btw). Naoto is definitely a great character, the man has guts and he doesn't let anyone let down to the ones he loves. It makes me want to hug him forever.