Eternal sin
However, the Church further believes there is no offence, however serious, that cannot be taken away by Baptism, or absolved from in the Confessional—that no one, however wicked and guilty, may not confidently hope for forgiveness. The Catechism says that Christ desires "the gates of forgiveness should always be open to anyone who turns away from sin." As did St Augustine, the Catholic Church today teaches that only dying unrepentant for one's sins is the only unforgivable sin. Indeed, in "Dominum et vivificantem" Pope John Paul II writes "According to such an exegesis, 'blasphemy' does not properly consist in offending against the Holy Spirit in words; it consists rather in the refusal to accept the salvation which God offers to man through the Holy Spirit, working through the power of the Cross", and "If Jesus says that blasphemy against the Holy Spirit cannot be forgiven either in this life or in the next, it is because this "non-forgiveness" is linked, as to its cause, to "non-repentance," in other words to the radical refusal to be converted. This means the refusal to come to the sources of Redemption, which nevertheless remain "always" open in the economy of salvation in which the mission of the Holy Spirit is accomplished."
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.