Rearrange

Botkawi has forever been in love with Praemai. His life is forever changed when a musical crystal ball he bought as an important gift for Praemai transports him back in time to the age of eighteen. Everything turns upside-down. Instead of fulfilling his hopes and setting things right with Praemai, Botkawi somehow ends up in the arms of Pisaeng. Thus begin their cat-and-mouse games with Pisaeng chasing after Botkawi. Old feelings for Praemai, however, become a detriment to their blossoming romance. Enraged, Botkawi keeps twisting the crystal ball in an attempt to get his desired results.

Both are BL dramas that has time travel, with the main character as a depressed/jaded working adult returning back to high school in order to fix things/fix his past. Rearrange is a Thai BL while Love for Love's Sake is a Korean BL.

Made by the same company. Both are in High School. Shades is a GL and Rearange has a side couple that is GL, Mint and Opal are a couple in both series. Flute who is the mc in Rearange is the director for Shades.