Party Broke Love

In a university, a boy found a girl in his department that he loves so much, even beyond the love for himself. The boy is in his finals while the girl is in her second year.

The girl's brother is also a student in the school but in different programme. The boy and his girlfriend are known or suspected to be dates as both of they does thing in common and are always together in the department and university.

It so happen on a bright day that a guy and his girlfriend decided to attend their departmental welcome party for the new students. Her brother came with them and they all sat on the same table catching the fun and hilariously talking.

The entertainment was served and it was so unfortunate that the girl was served first, as if the server decided to use 'ladies first' since she was the only lady in the midst of two guys (Her boyfriend and her brother).

With Love and Fun, her boyfriend jokingly asked his girlfriend to please take a meat out of the meal served her, meanwhile the meal was held by her boyfriend since she was attending to some issues. To his surprise, she said NO but the boyfriend took it as a joke. Then her brother asked for a meat too but she said NO because they were only two meats and she said her boyfriend has already asked for one.

While they were still joking, her boyfriend excused them to answer a call. In a little moment, he returned and found out that his girlfriend has eaten the meats. She was giving her boyfriend the leftover meal but he refused accepting it.

As they sat down, a friend of her boyfriend that was recently served came and gave him a meat in his mouth and left. Then his girlfriend was so so angry that she started to tap her hand on the chair warning the guy.

In the long, she told her boyfriend that she ate one meat and gave the other to her brother. Her boyfriend later left the party in angry and sadness, leaving his girlfriend and her brother behind.

Now the questions:

After the party, the two lovers has become different, so 

1. who is at fault; the boy or the girl?
2. how can this difference between the lovers be best resolved?
3. what is your advice to the lovers; individually and collectively?

Thanks.

V'3 & H+