Played this old game again, and outside of a few changes from the original not too much has changed. However enough has changed that my old walkthrough I made for this game to become out of date. So for the sake of those who do need help I will post an up to date one.
As before to get access to all the endings you will need multiple playthroughs seeing as some endings will need you to unlock a certain ending to get it.
Happy ending
You can get this ending on your first playthrough of the game. To unlock all you need to do is the following
1) When you are at the party when the choices comes up it doesn't matter. Meaning anyone of the choices will work
2) When the choice comes to help or destroy him comes up choose to destroy him
3) When it comes to asking whether or not you want to get Tom involved you must choose to get him involved
4) When it comes to telling Tom the choices choose the following choices
Make fun of his mother
make fun of his authority
tell him to calm down.
5) (Only if you choose the revenge option at the party otherwise ignore step 4) when the question pops up to give him his meds give them to him.
Follow all this and you will get the Happy ending
Unlocking the happy ending also unlocks the option of getting revenge against Samantha and Mark at the party for the Harem and Double Decker endings.
Peace for James
Like the Happy ending you can also get this ending on your first playthrough. To unlock it do the following
1) When you are at the party when the choices comes up just like with the happy ending you can choose any of them since none of them will deny you this ending.
2) When it comes to destroying or helping Mark choose to help him.
Do this and you will get the Peace for James ending
Double Decker + Harem
Double Decker is the second best ending you can get and Harem is the best ending you can get. In order to get this ending you will need to unlock happy End seeing as this ending is needed to unlock a critical choice to getting this ending. To unlock do the following.
1) When you are at the party choose the get revenge option
2) When the choice comes to either help or destroy Mark choose Destroy.
3) When the choice cones to either involve Tom or not you must involve Tom
4) When it comes to telling Tom the choices choose the following choices
Make fun of his mother
make fun of his authority
tell him to calm down.
5) When the choice comes to give Tom his meds or not you must choose to not give him his meds.
6) (Not need for the Double Decker ending but is mandatory for the Harem ending) When it comes time to let Melissa go or have one last fling choose to have one last fling.
Following this will unlock both the Double Decker and Harem endings
NTR Light ending
This ending for whatever reason isn't in the gallery. Like the Happy ending and peace for James ending it can be acquired during your first playthrough. Also unlike the older version of the game you can get this ending more than once without having to delete your save data. This ending is also critical for getting the Nightmare ending seeing as getting this ending will unlock the choice that is needed for it. In order to get this ending do the following
1) (Note this step only applies if you got the NTR Light ending already otherwise disregard this.) When you are at the party and your choices comes DO NOT choose "Get a Drink, wait and Follow if Possible." If you pick this you will effectively lock out the NTR light ending and lock in the Nightmare one.
2) When choosing to help or destroy Mark choose destroy
3) When choosing to involve Tom the choice here doesn't matter.
4) (Note this step only applies if you choose to involve Tom) If you choose to involve Tom when the questions come for what Tom to say comes make sure you get at least one of the choices wrong.
Following this will unlock the NTR light ending and will also unlock the choice that is needed to unlock the Nightmare ending.
Nightmare
This Ending is the worst ending you can get. In order get this ending you must unlock the NTR Light ending seeing as the NTR light ending. In order to get this ending do the following
1) When you are at the Party and your choices come choose "Get a Drink, Wait, and Follow if Possible" Anything else will effectively lock you out of this ending
2) When Choosing to help or destroy Mark choose Destroy
3) When choosing to involve Tom your decision doesn't matter however, if you choose to involve him make sure you get one or more choices wrong.
Following this will unlock the Nightmare ending.
Unlocking Chapters 2, 3, and 4 in the gallery
While these aren't endings they are something that can be unlocked and to unlock them you need to have unlocked the NTR light ending since the choice it unlocks is critical for unlocking these.
1) When you are at the party and the choices comes you must choose "Get a Drink, Wait, and Follow if Possible" as if you were going for the nightmare ending(Doing this will unlock chapters 2 and 3 in the gallery)
2) When Choosing to Help or Destroy Mark choose Destroy
3) When choosing to involve Tom you must involve Tom
4) When telling him what to say get all the choices correct. ( Doing this will unlock chapter 4 in the Gallery)
But on another note as I am not sure if the creator of this game is visiting this thread, but if you are if you don't already know this but the NTR light ending (Not sure what the actual name of this ending is) isn't in the Gallery.