Błędnie: Ever since I remember, he’s been always preoccupied by writing. Poprawnie: Ever since I remember, he’s been always preoccupied with writing.
Wyraz ‘preoccupied’ znaczy „zaabsorbowany”, „zajęty (czymś)” i łączy się z przyimkiem ‘with’, np. ‘They were preoccupied with preparing their wedding’ („Byli zaabsorbowani przygotowaniami do wesela”).