We learn about the punishment of flogging, which is the consequence for seclusion. Seclusion, and not intercourse. Simply transgressing the halacha that is a fence is enough to warrant this consequence. The appearance of impropriety is so important that some rabbis advocate flogging for being the victim of rumours about seclusion. They would even put a donkey's bridle on these people while they were being flogged. At the same time, the rabbis would call out the reason for the flogging.
The rabbis share a number of stories about how they overcame the urge to do evil. One was halfway up a ladder to have intercourse with a beautiful woman captured from enemies [and without having been completed her time to mourn the loss of her family]. He pushed his legs against the sides of the laser and yelled "Fire!" to draw the attention of others. Rabbi Meir was halfway across a rope bridge when he stopped himself. Another rabbi dealt with satan in the form of a woman who followed him. And one rabbi had sex with a woman he thought was a prostitute when it was actually his wife. He argued that he should still be punished because his intention was to transgress.
Can a man be secluded with his sister? With his mother? With his daughter? The rabbis argue about the dangers of seclusion, even with these relatives. Some argue that until the age of nine years and one day, girls might sleep beside their fathers. However, they seem to agree that it is when a child reaches puberty - when s/he becomes aware of and embarrassed about his/her nakedness, it is the time to separate family members.
One point early in our daf stayed with me - there is no need to worry about a woman being secluded with a man if her husband is present - or even within the same city. However, if she is friends with a man other than her husband (or if her husband warned her about seclusion with a particular man), she is not permitted to be secluded with him.
This suggests a couple of things. First, that the rabbis believed that friendship between men and women could lead to temptations and to sexual relationships. Second, the rabbis understood that men and women were sometimes friends. Men and women were friends; they did not live completely separate lives. This last point is an important fact to keep in mind as we read so much about the importance of separating men and women. Clearly, in real life, people were interacting across the sexes. The halachot suggest ways that people could live in order to minimize risk. However, that is not how people lived, even in the times of the Talmud.