Does one sin if he directs someone to pornographic websites, then that person enters them, influenced by the whispers of Satan, based on the Hadith: "The one who guides to good is like the one who does it, and the one who guides to evil is like the one who does it"?

You erred in your conversation with your colleague by speaking ill of an absent person, which is forbidden backbiting. You also erred by guiding him to a location of wicked films, which he apparently does not refrain from watching. You must repent to Allah and be diligent in avoiding what you have fallen into, and make your conversations abundant with the remembrance of Allah and speaking about what is beneficial. If you repent and strive to advise your friend to avoid these wicked matters, we hope that Allah will overlook your sins and forgive you.