HEY THERE!!! Spoiler warning for anyone reading!
Bad Ending 4 is pretty simple. Right after the river scene where Mychael carries you home and gives you clothes to freshen up, you're prompted with two options. 'I should be careful...' or 'I'm just being paranoid...' You have to choose the first option.
The next morning, when you both are sitting down for breakfast, you'll be prompted again with the option of whether or not to trust him. DON'T.
When he starts to lead you home, the choices don't matter much up until the mushroom circle, where after he keeps you from touching them and then yells at you, a third option appears labeled 'Call him out'
Pressing that will lead you to the 4th ending (Choices after that one can't change the course; they're all gonna get you where you're going.)
THIS ENDING HURT ME BRO.