Complex sentence: Shortly after recording his first album, he formed The Attractions as his backing band, they would tour and record together for the better part of a decade, though differences between Costello and members of The Attractions caused them to split by 1986.
Split into simpler sentences: Shortly after recording his first album, he formed The Attractions as his backing band. They toured and recorded together for the better part of a decade, though differences between Costello and members of The Attractions caused them to split by 1986.