The things which pain the most are :
1.Expectations...... because you didn't get what you wanted or things didn't happen the way you wanted them to.
2.Regret...... because you think that if you had done something at the right time, you might not felt gulity and regret the entire life.
3.Guilt....... because guilt is the strongest weapon which hurts you the most.
Pain of losing people you love, doesn't go away ever,you are just left with some faded memories,no one knows what future holds , so learn to respect and love people as long as they are with you because......then the only things left are regrets and guilt.