Did they feel great shame about sex and masturbation like many modern conservative Christians feel? Was it normal to have sex for pleasure? How was pre-marital sex viewed and how common was it? Were there double standards for men and women? Did married couples frequently have sex, or just for procreation?
Montaillou: Cathars and Catholics in a French Village 1294-1324
I think that this Micro-History of a small French village might be your best source for information on this topic. It is based on the extensive surviving records of the Papal Inquisition's investigation of heresy in the village, but covers many aspects of people's sex lives and the medieval conceptions of 'normal' relationships as well. And its a cracking good read as well.