Okay, there's a lot to address here. Actually, the Church does not loosely enforce this sin of fornication and adultery. It is a mortal sin in the eyes of the Church. And consider this. In your act of contrition you state the words "And I resolve with the help of thy grace to sin no more, to do penance and to avoid the near occasion of sin." How many Catholics take those words seriously? I mean, that being the case, then hardly any Catholic would be freed from sin. It's all meaningless. We are sinners. We have concupiscence we fight (the strong passionate desire for what God had condemned.) This notion is illogical. Think about this. You go to a priest for forgiveness of your sins. Your priest is acting in persona Christi (in the person of Christ). You have a girlfriend. She is sexy hot. You are weak because God has blessed you with a strong gift of testosterone. One thing leads to another, and boom you did it with her. Well that only opened the floodgates. Unless you're a Saint you're gonna fall again, and again, and again X10. You keep asking forgiveness. This one priest says it's a mortal sin. So you go and describe what's happening to another priest and he says it's a habitual issue and is only a venial sin, so you start doing your confessions with that priest so you won't be under mortal sin. That's a scary thought. But these two priests were acting in persona Christi yet gave two different opinions that are life-changing. BUT, the real answer is this: God is a God of love and mercy. You ask forgiveness and are forgiven. You ask to help you with the willful intent to change and go on with your life. It was Jesus who forgave you. That's all you need - Jesus.