Complex sentence: Jon takes Esther as his girlfriend, and even though neither has any interest in getting married anytime soon, and denies he is in love, but believes he really understands her and they can get emotionally lost in each other.
Split into simpler sentences: Jon takes Esther as his girlfriend, even though neither has any interest in getting married anytime soon. Jon denies he is in love, but believes he really understands her and they can get emotionally lost in each other.