Operação: Proposta de Casamento (2012)

Both about childhood best-friends falling in love

I recommend this both drama because , Male lead and Female lead
try to solve problem
In one drama explosion and another student murder/suicide

Both are time-travel drama because of their first love and the guy is trying to change his destiny and make the girl love and marry to him.

They're both about marriage, time travel and regretting your past, when I started watching "Go Back Couple" I immediately thought about "Operation Proposal" :)