it can also be that he fell in love with Viche, so he couldn't fall in love with the OG female lead, which brought the story of track. but yes, its highly likely that he did something to go back in time ლ(´ڡ`ლ)
But the thing is at the beginning he said he's been waiting a long time, so he probably had been studying how to go back in time probably?? (Like you said before)
Yeah im assuming he desperately tried to reverse time and then evenutally met the OG FL who helped him go back
My thoughts exact, he must have been trying to find a way to regress time for a long time and eventually found one with either the help of the og fl OR his uncle whose a “lunatic” and uses magic
So in the end,,, she'll never be able to go back into her own world cuz the ML had already fallen head over heels till death for MC (to the point of regression) .... Nicu~
The reason why MC wasn't able to go back to her world (despite following the story plot) was because ML died not long after MC was killed.
Either he used up his magic (and delved into the forbidden arts) to being MC back to life but it, instead, brought him back to the past.
Or
He committed suicide and then when he woke up, he found himself in the past (before MC went back in time).