Eternal sin
In Christian hamartiology, eternal sins, unforgivable sins, or unpardonable sins are sins which will not be forgiven by God. One eternal or unforgivable sin (blasphemy against the Holy Spirit) is specified in several passages of the Synoptic Gospels, including , , and .
Lust
Adultery: One of the main forms of lust seen frequently during the Middle Ages was the sin of adultery. The sin of adultery occurs when a person is unfaithful to his or her spouse, hence "invading of a bed not one's own," (Pg.235). Adultery is a special kind of ugliness and many difficulties arise from it. When a man enters the bed of a married woman it not only is a sin, but it "wrongs the offspring," because the woman now calls into question the legitimacy of children. (Pg.235). If a wife has committed adultery before, then, her husband will question if all his wife's children are his offspring. 
Simple fornication: Simple fornication is having sex with one's wife for enjoyment rather than for bearing children. Fornication is also sex between two unmarried people, which is also a mortal sin. Aquinas says, "fornication is a deadly crime," (Pg.213). Fornication is a mortal sin, but as Aquinas notes, "Pope Gregory treated sins of the flesh as less grievous than those of the spirit" (Pg. 217). Fornication was a grave sin such as that against property. Fornication, however, is not as grave as a sin directly against God and human life; therefore, murder is much worse than fornication. Property in this case means that a daughter is the property of her father, and if you do wrong to her, you then do wrong to him; therefore seducing a virgin or seeking pleasure from an unmarried woman is an invasion of a father's property.