I know this is a Yuri manga... But if you want me to feel sorry for Ayu in her position then you gotta give me a bf that isn't an overall nice guy or I'll feel guilty cheering for her.
I'm not an NTR person.
I'd like to have the guy's perspective in all this. Even if it's an "awesome a threesome" and I can hate him.
Ayumi is a good egg, she's just helplessly in love, Youko however needs a few lessons on how to treat people, you can't have everything you want in good conscience, that's quite egoistic