if u click here I have some very interesting.. facts for u !!!

Mieko used to play around with men's feelings during her teenage years, but eventually she got attached to particularly one.

Mieko messed around with a lot of guys because she wanted to be loved. She's desperate for it. She felt like she needed someone in her life to heal her from all the pain and neglect she got from her mother. Being alone drove Mieko insane.

Dazai also uses to mess around with women ,, BUTTT here are some reasons why ( yes these are headcanons don't hate on me guys😓😓 )

Dazai could never really stick with one partner because he couldn't find someone perfect enough for him.

he genuinely just got this passed down from his mother

Dazai is somewhat emotionally sadistic to the people he newly meets, but he's also somewhat empathetic in a way. ( his feelings are hard to describe because he can't describe them himself and neither can I )