Complex sentence: Jane is close friends with Jester, Pepper, Smithy, and Rake, and has a fierce rivalry with her fellow apprentice, Gunther, but most of her time is spent with Dragon, exploring tunnels in his cave, studying Dragon Runes, or patrolling.
Split into simpler sentences: Jane is close friends with Jester, Pepper, Smithy, and Rake, and has a fierce rivalry with her fellow apprentice, Gunther. But most of her time is spent with Dragon, exploring tunnels in his cave, studying Dragon Runes, or patrolling.