Need recommendations of a lowkey vibe romance drama (whatever region), not too depressing, with natural acting from the leads, shouldn’t feel forced or like they are acting if you know what I mean, need something similar to how Jung Haein acts in Something In The Rain/One Spring Night. 

Some dramas with this vibe: 

Something In the Rain, One Spring Night, To My Star(BL), The Reason Why I Dress Up For Love (JP) and  Our Dating Sim (BL). I want something where the lead actors are flexible and add their own little actions/sounds/mannerisms to the character, making the acting fun to watch rather than just reading the script. 

Dating in the kitchen
Because this is my first life
Run On
Do you like Brahms?

You can of course also try other works by the same director that did Somewhere in the Rain and One Spring Night. Heard It Through the Grapevine is a very fun and sweet family story about two teenagers that become parents and live with the family of the boy. This one has less couple moments like you are used to from Somewhere in the Rain and One Spring night though.
Something that has the same and if not more romance feelings is Secret Love Affair but this one is slightly more drama. She is a very famous person in the music world and his teacher. They start to have a love affair. It seriously is absolutely amazing how real their romance feels.