Around 440 is when the timeskip happened,pretty sure mo is angry at he tian for leaving him after middle school (because he tian promised to study abroad to his father)
I'm sure he's still angry. But also in love. His heart skipped a beat and he probably is avoidant of conflict and hopes for the best. I bet his frustration will come up again and at some point they need to talk about it.
When and why? Just one day mo was angry at him