Complex sentence: One of the instructors, sympathetic to his situation and believing he had some talent, suggested that he apply to Academies School of Architecture, but that would have required returning to secondary school, from which he'd dropped out and which he was unwilling to do.
Split into simpler sentences: One of the instructors, sympathetic to his situation and believing he had some talent, suggested that he apply to Academies School of Architecture. However, that would have required returning to secondary school from which he'd dropped out and which he was unwilling to do.