Emotions are the inevitable truth. No matter how you try to lie to yourself, cover it up, or suppress it, an emotion will always exist.
You seem like a logical, intelligent person. You're trying to figure out how to deal with these emotions in a way that prevents them from shaking you to your core.
So you want to be more emotionally strong. Unfortunately, learning how to CONTROL them is damn near impossible. That and the fact that you are going through puberty means your body is flush with hormones that can exacerbate moodiness. The whole point of having emotions is that they well up from your heart and no matter how hard you try to suppress them, they will inevitably rise to the surface.
I encourage you to consider this alternative: Instead of trying to suppress or control your emotions, become adept at dealing with them in a way that can be controlled.
Consider this analogy:
You're learning how to cook a new recipe. You have gathered all the necessary materials: tools, ingredients, etc. Now, the thing is, you'll probably completely mess up making the dish a few times until you discover the nuances of whatever ingredients and tools you're working with. It will take some time for you to mess up and learn what the indicators are for when to flip a burger, or how long to wait before adding an ingredient. These things will take time and practice.
I have shown this method to many of my colleagues and it has not failed me once.
You want to be able to deal with emotions? It will take practice, just like everything else you are going to try to learn. Want to become a "mack daddy"? You're going to have to practice, mess up, and learn from your mistakes. Want to learn how to do calculus? You've got to practice the methods until you have it figured out. Why not apply the same approach to learning how to deal with emotions?
You're sad because somebody put you down? I guarantee it will happen again, but you can use the opportunity to learn how to deal with embarrassment and humiliation. Try not to show weakness in public, of course, but you have to take some time where it is safe to just let the emotions out. Tell a friend, cry about it, write it down in a little black book. There is absolutely no shame in taking five minutes to feel truly upset about something. At first it will take a lot of time, but as you keep practicing feeling through emotions, you will learn what it takes to get yourself out of a rut. The only word of warning that I will give is that you must be very careful not to indulge in destructive behavior during the process, especially when learning how to deal with intense anger. The whole point is to learn how to deal with emotions in a platonic, if not constructive, manner. That means no breaking things, hurting people, or lashing out at innocent bystanders.
Yes, it sucks. Nobody wants to be in pain, but it is an inevitable consequence of life. Many people put up emotional defenses and hide behind ****y/funny routines to keep themselves from being vulnerable, but this also means that they are unable to form trusting bonds with people because they are always so worried that they'll get hurt. If you want to be able to truly FEEL any emotion, you'll have to be able to deal with ALL of them.
Youngmack, your heart is a muscle. If you want it to be strong, you will have to use it and have it work constantly.
When you find somebody to care about, I hope that you will put your heart into it. At the same time, when you do encounter pain and anguish, I hope that you are brave enough to face it and follow it all the way through. You definitely do not want to be *that guy* who is always bitter because he carries around all of his emotional baggage. You have a lot of people here who would be more than happy to lend their time and advice. There is not enough time in the world for it to be wasted upset about a past you cannot change. All we can do to be emotionally strong is to learn how to confront our emotions and move on.