1. Career planning and development direction are different: Yan Kun and Xu Nannan chose different career paths after graduation, which may lead to their breakup.

2. Differences in family background and values: Xu Nannan comes from a relatively wealthy family, while Yan Kun comes from an ordinary family. This difference in family background and values may lead to differences in their lives.

3. Long-distance love and busy work: Yan Kun went to work in Guangzhou after graduation, while Xu Nannan stayed in Beijing. This long-distance relationship may make their relationship more difficult. At the same time, their work is very busy, which may make it difficult for them to take time out to maintain this relationship.

Generally speaking, Yan Kun and Xu Nannan broke up for many reasons, including career planning, family background, long-distance love and busy work.