I second Protect the Boss he became really obsessed with her, it was hilarious.
I actually dropped this drama after first few episodes but I've picked it up again after some time and it gets better later.
Hi here are a few, Heirs When a man's in love A gentleman's dignity Cheongdamdong Alice
You said you don't have the time for a long drama, but if you ever do, definitely watch New Tales of Gisaeng for a male lead who is completely obsessed with his female lead o.o He goes to all sorts of lengths to be with her, it's kind of amazing...

For a not-so-typical set-up, I'd also recommend Que Sera, Sera. The male lead is obsessed with the female lead, but his obsession with wanting to be wealthy definitely complicates their relationship...
New Tales of Gisaeng sounds like a great idea, I'd like to try it this summer And I also dropped Protect the Boss, but since someone else seems to have appreciated it after giving it a second chance, I may do the same. Que Sera Sera and Chengdamdong Alice are dramas that have been on my list for some time now - I'll watch them, one of these days ;) And Q10 sounds really attractive to me right now. It may be my next choice after my exams, although I'm also hesitating between the Flower Boys dramas that have been recommended ;) And to those that recommended Secret: I'm at episode 15, and although the romance took some time to start, I've never seen one quite like it. I must admit the female lead, although there's nothing I particularly dislike about her, isn't the most amazing one I've ever seen - maybe the actress? She's good, just not too memorable. Him, on the other hand... wow! So intense, and unabashedly OBSESSED ;) Exactly the kind I was looking for. And I'm also not used to see, in a drama, such a brutal hero - although it's occasionally repulsive, the build up to the romance was great because of it, and the contrast with the way he is after, when he's in love and soooo sweet, is one of the most touching and intense things I've seen in a drama :) So thanks to MeiLi and mogwaid !
cunning single lady <<<
Secret Garden Heirs
Firstly, I'd like to add some recommendations myself: Summer's Desire -Both the lead guys fit your criteria perfectly. One of the most intense dramas I've ever seen. It's a bit on the dramatic side though. Plus both the guys are hot! ;) Ouran High school club - The format of the show takes a little getting used to but all in all it's funny and the lead guy kind of fits you criteria. It's hilarious but he does not realize he's in 'love', he thinks of his concern as a mentor-ish love. Sawan Biang - Kawee was the embodiment of obsession. Although it's a Thai drama so the lead being a douche and forceful is a given, but you do feel sorry for the guy eventually. And yes he's hot!!! Absolute Boyfriend - I saw the jap version and the male lead is exactly that - absolutely perfect! It's funny and romantic with emotional moments thrown in here and there. These are all off the top of my head, I shall add more when I remember. And please add more recommendations!!! Thanks!! :)
Hi My Sweetheart Sealed With a Kiss That Fool Autumn's Concerto My Lucky Star Dark Fragrance Too Late to Say I Love You
definitely protect the boss! he is head over heals for the female lead and is not afraid to show it. in fact he's very blunt about it
Thanks kdramaa - since I posted this I watched Protect The Boss, and I confirm his type of hero corresponds exactly to what I was looking for. So for anyone who is looking for the same thing as me, you should definitely try it :) p.s: I believe it's in this thread Que Sera Sera was recommended to me - one of my favorite dramas now! Hero is obsessed indeed (it takes a few episodes), but it's an obsession that turns destructive... So it's a great recommendation for anyone looking for a more realistic approach to the obsessed hero type!
In Oh My Ghost even though she's originally the one chasing him around, he eventually starts making up excuses to make him stick to him and all. He's kinda obsessed now.
Anymore recommendations since last year?