How can you break the cycle of emotional pain when involved with someone who's already committed?

How do narcissists perceive genuine happiness in others, and why does it confuse them so much?
Why do people hide their true intentions when they first meet a crush?
Why do people underestimate the discomfort of crowded events or extreme weather when the lure of something free or exclusive is involved?
Why is having fun crucial when learning guitar, and how does playing on a difficult instrument affect motivation?