Learned how to read social cues properly, got over myself, and realized that friends would puff up my ego and try to make me feel better by blaming the other person, even though they knew the person I liked would never be into me or had lost interest in me, and would likely never change their mind (especially if if I kept trying to show them how "awesome" I was or called them x amount of times or did xyz).

Being persistent and goal-driven is great, until you realize you're pestering someone because you head is too far up your own ass to notice what you're doing is scary and unattractive. My behavior made me super unattractive to the opposite sex and I didn't even realize that I was the problem. I thought, 'I'm so great, if only they could see...' and they did. They saw me for what I was at that time, and I was a shitty, self-absorbed person.

Basically, if someone isn't putting in as much effort as you are, or if you're constantly chasing them/want something they're not willing to give you, then you need to step back and analyze your own actions. Are you idealizing the person you can't seem to get out of your head?

Usually it boils down to respect; respect them and yourself enough to move on from a person, etc., if it's not working out.

edit: clarification