I just completed the game a while ago. It ended in a most illogical way. Upon finding that he is an alien, Jack Walters kills himself because of this "horrifying" knowledge. What`s so bad about being an alien?

maybe...... maaaayyybbbbeeee........ i really dont know aliens are awezome and shouldnt this go in general discussion?

It has a pretty big spoiler in it (namely that Jack Walters is an Yithian). I don`t know about the Cthulhu section of the forum but in The Elder Scrolls section, such threads with spoilers are moved into "cheats, hints, and spoilers" section.

SPOILERS:

Jack isn't a Yithian, but his mind was transferred to the Yithian world after he collapsed in the house. During those 6 years, his mind was transferred into the body of a Yithian, where he studied and lived in the City of Dreams for 6 years, studied, and learned. When Pnakotus was attacked, Jacks Yithian father decided it was no longer safe there and sent him back to the human world.

It's implied that on the night in which Jack was conceived the Yithian took over the mind of Jack's father, and in so doing, turned Jack into a half-Yithian. He possesses the psychic faculties of a Yithian, but the mental faculties of a human. Which is too much for a human's mind, according to Lovecraft lore. Thus the cosmic horrors which Jack encounters scar his mind, because he doesn't have a fully fortified mind.

In the end Jack is so frightened by the beings which he has encountered, and their even more terrible cosmic leader, that it proves too much for his psyche. Rather than continue to face the unveiled future, and find out what other horrors the world may be home to that your typical being does not know, he decides it's time to check out for good. Against the better judgement of the Yithians, the mental ward facilitators, and even what would be the choice of a sane Jack he ends it all.

Which is why in the sequels (had they been completed) Jack plays no role whatsoever, it's also why Jack was unable to vacate his mortal body and project himself into the future (like the Great Race can).

Given how many occasions there are upon which you might fail a Sanity check and commit suicide during the game (My personal favorite: walking out onto the deck of the boat and seeing Dagon sprout of the sea, rocking the ship like a bathtub toy. Jack says "Screw this." and blows his own brains out.), I don't know why you're surprised that this last revelation is what would finally drive Jack off the deep end.

Jack has something in common with a lot of Lovecraftian protagonists: he combines a strong will to live with a weak, credulous mind. When the latter breaks, the former follows.

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this explains everything lol