For all the endings achievements make sure to choose play the game in visual novel mode the second option and choose the special ending option the second option once again.
In order to get all (Jeff) endings in one play-through you have to choose these choices:
(It sounds interesting)
(It's annoying)
(Agree not to say anything)
(You want to make something)
(Ask Jeff about your idea)
(Let out the tears)
(Ask about it)
(Jeff can go first)
(Beg for her cooperation)
(Confront Jeff)
After you finish picking up all these exact choices both achievements for both endings will unlock.
Hope this helps!
Also check this perfect full achievement guide done by Cheevo Guides
