The male and female lead begin dating, but she doesn't take it seriously. Like maybe she will hang out with other guys and ditch the male lead, but not out of any bad thing. She doesn't cheat on him. She's just kind of dense and doesn't realize what she's doing is bad. She prioritizes others over the male lead.

Whooo, wait....your description sounds pretty specific to me. Just in case there's some sense of urgency here, I will give it a try, but this is a real challenge. The problem with Asian shows is that it's usually the guy who doesn't take dating seriously.

Lucky Romance  The female lead is eager to have sex with any man as long as he's born in the Year of the Tiger

Fool's Love She was the usual popular high school girl, now a national celebrity. He is an introvert and romantic fool,  but an ardent admirer of her. When they meet again, sparks fly. Only it takes time for her to understand he is not just a one night stand.

Kimi Wa Petto A weird story about an older career woman who takes in a younger male because he seems homeless. She treats him like her pet, washing his hair in the tub, cuddling with him at the couch and all that. Meanwhile she dates another man and doesn't think much of it.

I Do I Do This show has the usual k-drama elements: the rich glamorous boss, who doesn't think too much about the naive younger employee after a one night stand...except it is all in reverse. The female lead is the boss. 

@appleeye - Nah, I was thinking of different scenarios and thought it would be interesting if there was one like that.

Agreed. Like I said, it's a real challenge to find this kind of scenario in asian drama.

Bpoop Phaeh Saniwaat sounds like that. She is betrothed to the ML but doesn't love him at first and she becomes close to his bf/ SML which of course makes the ML jealous.

Go princess go 

Lovey dovey

When a man's in love

The eternal love

 Soumya:

Go princess go 

Lovey dovey

When a man's in love

The eternal love

Don't know about the other 3, but I've seen When a man's in love.

She straight up cheats on him in his own house in his closet with the other guy.

maybe, because this is my first life??? they're not the main couple though but they kind of fit your description