1__ Li Le's role in the drama: Li Le was supposed to be a couple with Li Weifan, but he gave up. He could also have been a couple with Zhan Yan, but he gave that up too. He completely gave up his responsibility and preferred to dance with nature. (That's why Zhan Yan is so angry when she returns to Ji's house: "Why am I so unlucky?" She still can't get out of control, so she loses her temper with Zhou's wife: "Why are you Xiao Hong's aunt?") But is Li Le really giving up so completely? He is determined not to put his clothes in the sun upside down. He also fell in love with Zhan Yan. So, Li Le will definitely show up later in part 2. Accept the result of fate.
2__ I think Li Le's appearance is to pave the way for Zhan Yan's transformation later.
Li Le is an optimistic, individualistic person, and I think in this drama, Li Le is the only one who can make Zhan Yan most comfortable. There is no relationship between them, and there are no demands or expectations between them. They, only then, seem like really good friends, without pressure, who trust each other.