I'm sorry to hear this. When you are alone or in your room, cry as much as possible. Don't restrain from crying. It's nature's way of accepting something hurtful has happened. It's also nature's way of allowing the healing process to begin.
Being always in the presence of your ex will prolong your healing and recovering from the breakup. However, there are things you can do to ensure you've healed and recovered from the relationship.
The first thing is to send your ex a test. Let him know you've accepted his decision. You won't force him to reconsider his decision. Thank him for the time you had in the relationship and wish him all the best. Through this method, you'll program your mind and heart to accept the situation and find ways of recovering from the breakup.
Spend time with your friends during lunch. You'll see him. But, tell your heart he is no longer your partner. He is just a friend like your other friends.
Only greet each other when possible. Nothing more. During discussions or group assignments, only talk about what you've been assigned. Don't throw occasional glances at him. Concentrate on the work you've been given.
It will be difficult to do these things because it's easier said than done. However, it is possible.
The most important thing is to reassure yourself that you will come out of the breakup in one piece. You won't accept to be affected by the relationship in negative ways. You'll do all you can to ensure you've healed and recovered from the breakup.
Don't be angry at him or hate him. You've been angry at him and hated him. Now, it's time to get rid of the negative emotions. Tell yourself entertaining the negative emotions won't help you in any way.
Ask your classmates to watch over you. To remind you that you have a beautiful future in front of you. That you need to concentrate on your studies and forget about your ex. Friends can help you to heal and recover from the breakup.
If you believe in God, pray to Him to help you to heal and recover from the breakup.
Stop listening to any love songs. Throw or tear away his photos or delete them. They are no longer beneficial to you. Unfriend or block your ex from your social media sites.
Don't pretend you're okay. There are times you will break down. Nonetheless, be determined you will get over the breakup.