1) "She suggested to go on a break while I was studying for my finals. I stupidly agreed. 18 Days later I reached out to her again, but the tone of her messages changed dramatically, that was when I realised something was wrong."
Always trust your gut instincts.
She lost attraction to you and probably started developing feelings for a new guy. It's also very likely that she also started a new relationship with this said guy, even if it was just an "emotional affair".
2) "My heart sank, because it was what I feared."
Never be afraid to lose a woman. Never be afraid to walk away. Being afraid lowers your self-confidence. You have to be in a position in life that even if your "soulmate" decides to dump you, you can easily find a new quality woman to spend time together.
3) We talked, we cried.
Women want stroing, stoic and independent men.
You are her rock; her sounding board for insecurities and worries and fear. Her soft place to land.
She isn't your rock. You do not bring your doubts/fears/insecurities/deep problems to her. You may get the quick ego boost or reassurance that you're looking for, but you are killing her attraction for you.
4) "promised that she should would find me in 2/3 weeks as she needed to separate the feelings of "boyfriend" and "friend" towards me. As we left she accidentally called me by my pet name and pinched my cheeks."
She put you back to the friendzone while she is sleeping/will sleep with a higher value man.
5) Three days later (24th May) I sent her an email
You broke No Contact to pursue your now ex-girlfriend.
6) What do I do friends, What am I doing wrong?
A woman will think a hundred times before dumping you. She will start acting cold and distant. She will stop calling you cute names, and will stop chasing you. All the signals will be there, but most men will avoid them. We don't want to face rejection.
When she finally decides to dump you (often AFTER starting a new relationship with a different guy), the odds that she will get back with you are close to nil.
At this point, she most likely lost all the respect and attraction for you.
You have to work on yourself, and become a better man. Lift, meditate, read, buy new clothes, study harder, invest in your career. Avoid drinking and partying for a while. Start new hobbies and seek friendship with other guys interested in becoming better men. Avoid losers if possible.
"The secret is not to run after the butterflies ... take care of your garden and they will come to you."