Complex sentence: She foolishly believed him and, when her trust began to wane, spread the blood on a shirt and gave it to her husband, who died slowly and painfully as the shirt burned (either in actual flames or by the heat of poison) his skin.
Split into simpler sentences: She foolishly believed him and, when her trust began to wane, spread the blood on a shirt and gave it to her husband. Hercules lay dying slowly and painfully as the shirt burned (either in actual flames or by the heat of poison) his skin.