Please Explain! (Spoilers)

Here are some answers to your questions. (SPOILERS)

1) The whole religious theme (Jack, Marieclaira). What was that all about?
Obsession, a psychopathic trait:

It is a common trait for a psychopath to become obsessed with something. In Nigel's case he chooses the Templar myth of Maraclea.

One Example of the ‘Maraclea’ myth (there are many versions – google for more):

"A great lady of Maraclea was loved by a Templar, A Lord of Sidon; but she died in her youth, and on the night of her burial, this wicked lover crept to the grave, dug up her body and violated it. then a voice from the void bade him return in nine months time...” “He obeyed the injunction and at the appointed time he opened the grave again and found a head on the leg bones of the skeleton (skull and crossbones). The same voice bade him 'guard it well, for it would be the giver of all good things', and so he carried it away with him. It became his protecting genius, and he was able to defeat his enemies by merely showing them the magic head. In due course, it passed to the possession of the order."

Reasons Nigel chooses the Maraclea myth as the object of his obsession:

1. The re-enactment of this myth, would satisfy his Sociopathic urges for ownership, control and power.

2. Nigel’s father was a member of a Brotherhood with Templar roots. This Society occupied all his time and left none for his own son. Nigel wanted to believe this was justified but try as might, he could not see the society as anything more than pathetic “male bonding”. It made him deeply angry that something so unimportant had such a huge impact on his life, so he became fixated on making the society matter. By possessing the skull, Nigel believed he could restore this Templar based society to its original medieval power and glory, as per the myth.

How the playing card fits in:

Within Nigel’s delusional world, he literally sees the images on the Jack of Spades as an illustration of his relationship with Alex. He interpreted them as proof of the inevitability of Nigel and Alex’s coming together, to operate as one and how this partnership would bring them ultimate power for eternity.
This is what Nigel thought the images on the card represented:

The Spade (the head of a spear) = Himself, a tool for killing.

The Jack (knave/rogue) = Alex, his partner.

The “eternity” symbol on the hand of the Jack = the inevitability and permanence of his relationship with Alex.

2) Why did Nigel kill all those people?

Nigel only killed one person - Susan. He kills her because he wants to give his “partner” (Alex) the chance to obtain the power as layed out in the Templar myth. He saw Susan, as Alex’s true love.

3) Who was the woman in the photos? Nigel's mom (or step-mom? What was that all that about?

The photos are of Nigel’s mother. Nigel had sent them to the society in the hope that they would set in motion a chain of events that would unhinge his father. This ultimately results in his mother’s death, which plays into Nigel’s hands, as his mother is his one true love. So, Nigel sees his chance to get “their” Maraclea, particularly as he couldn’t be certain whether Alex had fulfilled his request at the morgue.

4) Why did Alex take Susan's head and why didn't he cover the tomb?

Alex digs up the grave and takes the skull to make it look like he is re-enacting the Templar myth. However, all he cares about is toying destructively with Sally, not the power of the skull. She is his new psychological “victim”. His plan was to publicly humiliate Sally and cause her to loose any ounce of professional credibility. He waits for her to have her day in the sun so he can rip it away. To a Sociopath like Alex, this is the glory.

5) Is Alex to blame or not, I mean, was he lying to the psychologist cause in the end she says "this sick f*uck" or something referring I suppose to Alex or did Nigel's spirit got into Alex?

Who is to blame? Gestalt is to blame, as without this condition nothing would have happened. It was the combination of Alex and Nigel that created the lethal mix.

Alex is affected by Nigel, however it is at a psychological level, not supernatural. Nothing in the back story is a lie. So everything he tells us about what happened with Nigel and who murdered whom, is true. The power struggle Alex describes (that leads to Alex’s unhinging), is a typical part of the dynamic of this sort of Gestalt relationship.

When Sally says “Evil little *beep* she is realizing that while Alex didn’t pull the trigger, he is equally responsible for creating the fatal psychological environment.

I know this was written several years ago but I was hoping you could help me understand something.

For one, what did you mean when you said this: When Sally says “Evil little *beep* she is realizing that while Alex didn’t pull the trigger, he is equally responsible for creating the fatal psychological environment.

How was he responsible for that? Do you mean because he sort of kept pushing inside of Nigel's head and that pretty much put them together as one person? I guess the card thing got me really confused because I wasn't sure what he was trying to say. My only conclusion was that he was lying about stuff (though I know from another board or this one that his story was all truth). It just baffled me and I don't like not understand ha.

Also, what was happening during that train station thing right when the gun is held up to Nigel? I know part of it is that he wants to die and sort of merge with Alex, but what else was he trying to say? I can't remember word for word but I know that scene had another meaning..

Why not try watching it again.