Below is a quick guide for all the endings.

Bad End 1: The Other Side

There are 2 ways to get this ending. When prompted, keep looking out the window. 

Bad End 2: His, Once Again

Search the drapes and take the opportunity to strangle Kas.

Bad End 3: Something Important

Search under the pillow and poison Kas.

Bad End 4: All Alone

Search under the pillow and poison yourself.

Bad End 5: The One... Or Not?

Don't attempt to kill Kas or yourself, and don't look out the window. Have below 3 affection at the garden. Here are some choices you can make for this ending:

"Who are you?" / "Where am I?"

"..." (Don't choose "Let go, please.")

"How do I leave this place?"

"It's beautiful."

Bad End 6: Eternal Bloom

Don't attempt to kill Kas or yourself, and don't look out the window. Have below 5 affection at the garden. Here are some choices you can make for this ending:

"..." (Do not pick "Who are you?" / "Where am I?")

"Let go, please."

"Why can't I remember anything?"

"This isn't real."

"Trust him."

Normal End: 

Don't attempt to kill Kas or yourself, and don't look out the window. Need 5 affection to progress. Affection choices below.

"..." (Do not pick "Who are you?" / "Where am I?")

"Let go, please."

"Why can't I remember anything?"

"This isn't real."

"Pretend to trust him." / "Don't trust him."