She is frustrated of me, what do to next?

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She still does loves me, cares me but she says that she is so much frustrated coz of my habit. My possessiveness is the main reason for this. I can't tolerate her when she shares her private lunch with her one of the classmate who is male. How can i tolerate that she shares her biscuits with a boy leaving other girls in the class room. Not only this i am possessive in many things. As she told me that she was frustrated of me and tired of me, she haven't come front to end our relationship. I don't want this relationship to end and i know neither she wants. But since week ago she acts to me very much differently. What to do next please help me.