Why do we sometimes treat people differently once they become more important in our lives, and how can we avoid that in relationships?

What strategies do people use to cope with the feeling that life is just a farce filled with suffering?
Is our life really made for suffering and not happiness, or is it we humans that make it so bad and awful, and can it be filled with so much happiness and joy?
What should you focus on instead of trying to change someone's mind about dating you?