Making out is a mortal sin since it gives rise to sexual passions.
According to a decree of Pope Alexander VII in 1666, a kiss is not “merely a venial sin when performed for the sake of the carnal and sensible delight which arises from the kiss, even if the danger of further consent and pollution is excluded.”
– Alexander VII, “Condemned Decrees” proclaimed on the 18th day of March in 1666 (Denzinger 2060, 1140 40).