Complex sentence: Failing to impress, he immediately moved back to Benfica, where he would play for the next three seasons; he spent two final seasons at Boavista, ending his career during the 1984--85 season to become team coach.
Split into simpler sentences: Failing to impress, he immediately moved back to Benfica, where he would play for the next three seasons. He spent two final seasons at Boavista, ending his career during the 1984--85 season to become team coach.