Secret Love Affair: Not exactly a "slice of life" type of drama, but I think it's still fit well what you are thinking very "adult" drama and really bittersweet all along with some sadder parts. It's really a must watch! (and top notch actors)
I'm more wary of recommending you this one, but
Please Come Back, Mister might fit what you are looking for. The plot is quite complex, it does have some good thriller elements too (the synopsis really doesn't do this drama justice). It has a lot of comedic moments, but it also revolves around more serious or darker matters and gets quite sad especially toward the end. It's still overall a comedy, but no "stupid" happy ending (there's no way it would have worked with the plot anyway).
