Second issue: Losing a friend

We all have been through some rough times, but one of the hardest is when you lose a friend that is close to you. Be it death or their choice that they just don't want to be friends anymore, it's still a sensitive topic, and can be very hard, especially if you don't see it coming.
The first thing I would recommend, is learning to deal with the loss. If they have died, think of all the times you were together and had fun, and treasure those memories. If they have just left, it may help to think of the positives to their leaving. For example, they always lied to you, or they didn't consider your feelings.
After you've coped with the loss, keep your mind clear of them. If you continue to think about them during important times, it may fog up your mind and make it impossible to focus on the task at hand. This step is very important, especially if you feel a bit of anger toward the person. Nobody can do things quite the same while angry as if they were happy while completing the assignment. If you encounter the friend again after they have left you, consider your options; you could nod a hello to them to acknowledge their existence, or you could ignore them and go about your merry way without them. If your friend has passed away, no matter how hard it is for me to say this, but I'm sorry... they will never come back. However, you always have them with you in their memories and your heart. Carry on your life for them, and think about the fun times you had together when you miss them. In these cases of your loss, there's nothing wrong with crying from time to time. It will help you release stress and you'll feel much better after getting your emotions out. However, if you feel sad for a longer amount of time then you should (example: no longer being friends, a week or two, or a death of a friend, more than a year) you may be experiencing depression. If you feel you've become depressed after a loss, ask for help as soon as possible.
We all go through those days where we wake up and realize "wait.. I'm not friends with them anymore.." and feel a little guilt, but it's not your fault. If they didn't like your personality, then that's their loss, not yours. Just remember that you'll always have your memories, and no matter what, don't change yourself for someone else.