I've seen that in a few dramas. The male lead will have an ex who left him to be with someone else and because it didn't work out, she comes back for the male lead. By that time though, he's fallen for the female lead. Well, are there any where that girl who leaves him IS the female lead and it deals with her regretting breaking up with him and tries to get him back? He's cold towards her, but in the end they get back together.

 jak:

I've seen that in a few dramas. The male lead will have an ex who left him to be with someone else and because it didn't work out, she comes back for the male lead. By that time though, he's fallen for the female lead. Well, are there any where that girl who leaves him IS the female lead and it deals with her regretting breaking up with him and tries to get him back? He's cold towards her, but in the end they get back together.

If i understand your question correctly these will be my suggestions from  the dramas i have qatches are only these two.

Emergency couple - They both fell apart in this drama in the starting but im guessing this can come in according to your question.

And my second guess is Heartstrings

I've never seen it, but Cunning Single Lady has a main couple that divorce (summary suggests it's the female leads idea), and then she tries to get him back (revenge vs. sudden wealth). 

Cunning Single Lady sort of fits, she doesn't leave him for somebody else though, there are other reasons.

 Samantha:

I've never seen it, but Cunning Single Lady has a main couple that divorce (summary suggests it's the female leads idea), and then she tries to get him back (revenge vs. sudden wealth). 


 Meg:

Cunning Single Lady sort of fits, she doesn't leave him for somebody else though, there are other reasons.

Yeah, I want it specifically that she left the male lead for someone else.

Not exactly what you want cause the main female lead is not the one who leaves him for another man, she is her stepdaughter. But i believe you'll like it so you should definitely try Innocent Man.

 Serin:

Not exactly what you want cause the main female lead is not the one who leaves him for another man, she is her stepdaughter. But i believe you'll like it so you should definitely try Innocent Man.

I didn't really like Innocent Man. Couldn't get into it. Yeah though, if the woman who ditched him was the female lead and they got back together, then it would fit perfectly.

https://mydramalist.com/9137-my-sunshine - The Female lead leaves him for other reasons, but gets married to another man and then comes back  to the male lead's life.

https://mydramalist.com/9939-yah-leum-chan - I havent seen this, but I think this Thai lakorn fits your requirement.

 Ansuya:

https://mydramalist.com/9137-my-sunshine - The Female lead leaves him for other reasons, but gets married to another man and then comes back  to the male lead's life.

https://mydramalist.com/9939-yah-leum-chan - I havent seen this, but I think this Thai lakorn fits your requirement.

I'll check them out. Thanks.

Princess Agents - Somewhat as you described, ML and FL had a budding relationship / complicated attraction, but due to extreme circumstances FL leaves him and stays with the SML. SML has romantic feelings for her, which she does not return (although she cares about him). ML acts coldly towards her while sorting out and eventually coming to terms with his feelings for her. In the end the FL realizes her true feelings for the ML and goes to him. Dramatic events ensue. Warning, it ends in a cliff hanger and I don't know if they're making  a second season.

It's a bit more complicated than just "A and B are a normal couple, B leaves A for C, B regrets her decision and tries to win A back, A acts coldly towards her, eventually A and B get back together". 

I think you might like Summer's Desire. It's really similar to what you're looking for.

 Serin:

I think you might like Summer's Desire. It's really similar to what you're looking for.

I really didn't like it. I hated how it changed male leads midway through.

 jak:

I really didn't like it. I hated how it changed male leads midway through.

Lol but you know, she leaves him and goes back to him again. Just like you wanted. :)