According to Catholic teaching; how long do we go to Hell for? When people are sent to Hell, is it really for eternity, or does the amount of time spent in Hell depend on the Sins/Crimes committed on Earth?

I find it difficult to accept/believe that people who do not believe in a Book (the Bible) in a World where every man lies through their teeth just to sell you something or just to manipulate you because they have their own agenda - will go to Hell for eternity.
In the Catechism of the Catholic Church statement on hell, we find the following:


  The teaching of the Church affirms the existence of hell and its eternity. Immediately after death the souls of those who die in a state of mortal sin descend into hell, where they suffer the punishments of hell, "eternal fire." The chief punishment of hell is eternal separation from God, in whom alone man can possess the life and happiness for which he was created and for which he longs.


The 'In Brief' recap summarizes this as:


  Hell's principal punishment consists of eternal separation from God in whom alone man can have the life and happiness for which he was created and for which he longs.


So yes, Catholic teaching is the traditional view of hell, that which is described as 'eternal conscious torment'.