I met a trendy Christian girl

[Sethomas]

Depends on whom you ask. In conventional theology, sinfulness is a deliberate separation from God undertaken by the individual. So, damnation is not God's doing, but a de facto reaction for dying outside of His grace. Id est, you choose not to go to heaven. Hoewver, what is or isn't sin is determined by God alone. So, you detach yourself, but only God knows if you are detached.