Trust me. I totally get how you feel. My adivice to you is that you should make a list of things you are good at that will make your heart feel warm inside and you dont need a/o to do these things, even your boyfriend who used to mean the world to you. stand in front of the mirror every night and say these sentences out loud to yourself. Then it would put a real smile on your face and whenever you feel broken, take out the list and read it. After a while, You dont need to pretend to be happy, you will be happy because of how talented you are and what a great person you are. Wherever you are able to see it, put pix of fun times with your friends that will make you smile (for real) and thik about that happy memory. A lot of artists make music that unleashes their pent up emotions about how they felt when certain things came thier way, such as Grenade by bruno mars. And try to do things with friends so it will distract u from being depressed. Remember: if your boyfriend is a loser, losing a loser is a good thing!!!
Keep smiling!!!