"I loved you."
The L appears only with second person conjugation: szerettelek (téged) or szerettelek titeket (these are also correct translations). With "ön" you use third person conjugation, so there's no L.
Right. That makes sense; thanks. I posted my original comment from the mobile app after being asked to translate "I loved you" from English, typing something like "*szerettelem" (or maybe actually the correct szerettelek), being told it was incorrect, and only being shown "szerettem" (without the önt!) as the correct answer.
The fragmentation of variations on a task, their correct responses, and the related discussion threads can be very confusing!