Responses
I think making a move on your teacher is a lot lot harder than on a fellow classmate, which is already hard if you're both guys... I am like 99% certain the person he loves is not the teacher. Why would he receive his teacher's wedding date on his phone?
I think the setup we are getting is "I loved some older family friend / cousin / etc. and am heartbroken and then will end up in the arms of the teacher instead." Although, in these sorts of situations the teacher is only a temp for another student (think Someone Else's BL Manhwa)

Kwon Yuri is done with all their drama. But when will he act on his feelings towards the teacher??? (づ ̄ ³ ̄)づ
See, Yuri don't put that face. You are in the same situation, my brotha ╮( ̄▽ ̄)╭