Gravely sinful? That's not even in the 10 commandments. Killing somebody is gravely sinful. Rape is gravely sinful. Im catholic so I'm not trying to mess w you. If there's 2 people that like eachother and decide to have sex, do you think god is gonna be pissed? You have sex before marriage and then you can't get into heaven, you go to hell? Alot of people do this.