For some reason my computer is bugging and I can't see what you've already watched, so sorry if I recommend a drama you've already completed!
I second I Need Romance 3, because he does get "jealous" quite early, only he doesn't handle his jealousy exactly the same way as other male leads do in most dramas (don't want to reaveal too much, but let's say his jealousy doesn't make him act too impulsively, he leaves the female lead some space)
In the chinese dramas Lady & Liar and Cruel Romance, both male leads get extremely possessive (and therefore jealous) of the female lead very early (way before she falls in love). The male leads in these dramas, especially Cruel Romance, were too macho for my taste, but of course that's only a personal opinion. Sealed With A Kiss has a similar character, but even more intense (he's definitely the most irrational, possessive/jealous male lead I've ever seen in a drama), if you like that type of character.
In Autumn's Concerto, if I remember well, the male lead does get jealous at the begininng of the drama. But the drama is pretty much cut in half because he loses his memory (nope, not a spoiler hehe, it's written in the synopsis, I checked), so his jealousy reappears but only later in the drama.
In Boss & Me, the hero, a large company CEO, falls for a small employee very, very fast. This drama is all clichés, but it's enjoyable because it's well executed, and it focuses purely on the romance, nothing more. He gets jealous in the beginning because her attention isn't on him, even though he's already in love.
In Discovery of Romance there's a lot of jealousy because the whole drama is about a woman torn between her current sweet boyfriend, and her attractive ex. But maybe that's not the kind of jealousy you're looking for.
In Myung Wol the Spy the male lead gets terribly possessive, but only in the latter part of the drama. For the first half of the drama he's the most unsympathetic jerk ever, but it's so satisfying to watch him fall in love, and hard (actually there's one scene that's quite disturbing where the intensity of his feelings, his possessive tendencies and his insecurity push him too far in my opinion).
In Protect The Boss the hero falls for the female lead within the very first episodes and wastes no time denying it. However his cousin and business rival also becomes his love rival, which triggers jealousy and possessivene feelings.
I can't quite remember at what point the male lead in The Greatest Love falls in love, but I remember his chacacter falling very hard and being jealous and possessive for a good part of the show, because of a charming doctor that is also courting the female lead. These two are in some kind of romantic reality tv show, so practically the whole country ends up wanting them together, and the male lead has to fight against this ;)
I nevr finished this drama, but I believe the male character in What Is Love turns out to be the jealous and possessive type -- he starts as a player, but he rapidly falls for the female lead after tricking her, and from what I saw (I skimmed through it), he spends the rest of the drama trying to prove his sincerity and brooding because, like in The Greatest Love, the female lead and another man are on a romantic reality show.
Hope you find something you like!
