SPOILERS:
1st ending - Marlowe die with the infection
-Treat Niall badly during the game
-During the "father conversation" with Niall (day 9), any choice will lead you to this ending
2nd ending - "Until death do us part"
-Treat Niall well during the game
-During the "father conversation" with Niall (day 9), any choice will lead you to this ending
3rd ending - You drown in the lake
-Treat Niall badly on day 6
-Choose "A lovely day to spend with Niall" in day 7
-On day 9, during the "father conversation" with Niall, choose "I doubt you actually know what a great father is, Niall"
-Lose in the "a" "d" system
4th ending - You get rid of the infection
-All the process in the 3rd end, but win in the "a" "d" system to get out of the lake