Need a kdrama where couple don't end up together quickly, they take a lot of time.

So, I need drama where male and female lead don't end up quickly, as in they take a lot of time to get together, because-

Male lead is confused with his feelings between two girls 

Girl loves him first, she stays by his side.

Male lead tries to fight off his feelings for her, but didn't want to admit. Like Another Oh Young's male lead. 

Second male lead should not give me second lead syndrome too much. 

Also, please no unnecessary love triangle between two guys and one girl, cause I would literally vomit if I saw that kind of love triangles again in my life. 

Dramas which were of my taste are-

My name is Kim Sam Soon (literally enjoyed him fighting his feelings for Sam Soon when he already had a girlfriend.)

Rich Man, Poor Woman(They took so much time to get together lol)

 Coffee Prince ( This just seems to be the almost exact drama of my taste. I am still watching it though.)

Warm and Cozy(didnt exactly like male lead but it had trope which I enjoyed.)

Time we were not in love (they couldn't have ended up together any later lol.)

Secret life of my Secretary (Would prefer it very much if more female leads can be like her, Gentle, cute, feisty, understandable lol)

So, please please recommend me something good to watch! Please, I am dying to see kdramas of my taste. I've been deprived so long! 

Please not more than 30 episodes, 1 hour each, drama. I lose my dedication in long dramas, that's why!

Story of Ming Lan, the definition of build up and slow burn, they get together in the 2nd half... if you don't watch historical dramas, let this be the one!! But, it's not so much the MLs feelings (when he knows, he knows, it's just timing), the FL is what you want though and don't have any worries about the 2nd ML.

oh wow I was gonna immediately recommend rich man poor woman because I just rewatched it two days ago, but then you listed it XD

• it's been a hot minute since i saw it, but i'm pretty sure Buzzer Beat is like this? but tbh all i remember is the fantastic kiss scene oops
• I second K2
• Also a Ji Chang Wook drama, Suspicious Partner involves two people who had been cheated on in their last relationships. She falls for him first, but he is still hung up on heartbreak so it takes him longer to accept that he has feelings for the girl. No second male lead. 
• I think the plot of Full House is like this? (i prefer the thai version) it's also been a while since I saw them but I'm pretty sure they fake get married to make his ex-girlfriend jealous and they fall for each other as they're living together
• when i was going through my list for dramas, i focused more on the male lead tries to fight his feelings for her point you listed. Introverted Boss is like this (when you get past the first five episodes because the writers listened to viewer complaints and changed the direction and pacing of the drama). He fights his feelings for her because her sister died while working as his secretary and he blames himself and doesn't think he has the right to love her, you know the deal. She hates him at first because she is under the impression that he was the reason her sister died but that gets cleared up and once she realizes he's not a bad person, she becomes his number one supporter and helps him overcome his social anxiety. 
• I'm Not A Robot kind of does this with a different twist - he fights his feelings for her because he is under the impression that she is a robot and not human
• A Korean Odyssey this is going to sound absolutely ridiculous because it's a fantasy drama, but i have no idea how else to explain it: he fights his feelings for her because he is a monster and her blood is special and he has to kill her in order to become stronger but he ends up falling for her instead
• not a kdrama, but Autumn's Concerto is kinda like this -- most of what i'm about to say is in the synopsis but i'm putting a spoiler warning just in case: so basically within the like first five or six episodes they meet and fall in love in college, but then he loses his memory, most of the drama takes place about seven or so years in the future (present day) when they meet again and he doesn't remember her and is engaged to someone else, she still loves him and he starts to fall for her again -- there is a "love triangle" but the second dude very obviously never has a chance for the main girl's heart and is moreso there as a supportive friend
• also a Taiwanese drama, Just You is about a boss who makes a no-dating rule at his company because at his last job he had his heart broken in an office relationship, but then he ends up falling for one of his employees.
• Oh My Ghost-ish? he has feelings for another woman at the start but i don't remember how long they last for or if they were really a source of conflict
• I know there is a japanese movie shoujo adaptation out there with a plot like you described above but I can't remember. Heroine Disqualified? or maybe Strobe Edge?
• I haven't seen it myself, but I would look into Chocolate the synopsis sounds like what you're looking for

Sorry I couldn't exactly hit the mark, but I hope this helps!

1.  My princess (they don't end up together quickly, both are in love with someone else at first, second lead syndrome isn't strong)
2. Goong (FL falls in love first, he loves another girl and makes the FL wait A LOT, there's a 2nd ML but I personally didn't like it so I would say 2nd lead syndrome isn't strong)
3. My girl (2005) (FL falls in love first, he's still in love with his ex and for many reasons they don't end up together quickly BUT 2nd lead syndrome is quite strong I have to say... however the leads are perfect for each other and it is one of my favorite drama so... Your choice) 
4. Fated to love you (he is still in love with his girlfriend, for many reasons the leads get together quickly but they have a real happy ending only at the very end because many things happen. There's a 2nd ML but it's clear he and the FL weren't a match)
5. Full house (he's in love with another girl, the leads live in the same house but have an happy ending together only at the very end. 2nd lead syndrome wasn't strong fro me in this one)
6. My girlfriend is a gumiho (FL falls in love first and sticks to him all the time but he loves another girl, they take a long time getting a happy ending. I liked the 2nd ML in this one but didn't see him and the FL together)

That's it, I hope it will help you!! :)