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*UPDATE* I've found the movie, it's an Australian movie titled Contagion (1987). Thanks you all for the help! https://www.imdb.com/title/tt0123733/?ref_=kw_li_tt I've removed the ending from my original description of the plot so I don't spoil it for those interested in watching it.
I saw a horror movie when I was a teenager and I remember it very vividly but I can't find it anywhere after months of searching. The fact that I remember so much about this movie and still can't find it is driving me insane. I guess some hardcore horror fan might know it. Here it is what I know and remember. Considering my age the movie is from the 70's or close.
In the movie, a guy is driving his car on a road that goes through some woods. Suddenly a beautiful naked woman runs in front of the car while screaming for help. Immediately one or two men who looked homeless and were after her grab her and start beating her brutally. The guy in the car tries to do the right thing and stop the crazy homeless men but he fails and the men beat him and rape him too, against his car. I remember that one of the crazy men is very dirty and creepy and puts a mask over his face while raping the guy.
Later, our protagonist wakes up and he discovers himself in some kind of camp. Next to the fire he sees the two crazy homeless men (maybe they were more) and a couple of naked girls who are unconscious or dead. He talks briefly with the homeless men and he realises they're completely delusional. He escapes and finds a huge mansion, where an older man lives with his beautiful wife and daughter. The protagonist is seduced by the luxury of their lives and the beauty of both the wife and the daughter.
The millionaire begins explaining the guy how he makes money. And he shows him he has a computer (very old computer and operating system, this was before Windows) where he makes online transactions. He shows him that he is able to earn millions in seconds by taking advantage of differences in the price of currencies in different countries. Secretly, the protagonist has sex with the millionaire's wife. I'm not sure if he had sex with the daughter too but I think there was some flirting at least.
The protagonist resumes his normal life but from time to time he goes again to visit the mansion in the woods. The millionaire and his family continue to poison the guy's mind with greed and lust, convincing him he's a winner and he should do whatever he wants. He becomes crazier and crazier until he starts killing people. I think I remember a scene where the protagonist has an argument with a colleague or friend in a gym, he kills him and escapes.