Salaam Alaykum, I had a conversation with an Ibadi and he said major sinners will be in hell forever and he cited Al Baqarah 81-82. How do we understand this verse?

The ayah says and his sins engulf/encompass him and this is the case of the disbeliever not the believer, also Allah told us in the Quran that he forgives all sins except shirk and we believe what Allah told us.