Hello, I've  watched a lot of drama and i don't know what to watch next.

can you suggest me a kdrama without love triangles and with an happy ending?

I prefer romantic comedies without too much drama, no historic dramas (I've tried but I've never really liked one a lot), and no noona dramas.

I hope that someone can suggest me something I've never watched!

Thank you :)

I just finished Bring It On, Ghost a few days ago and it is so so adorable! It fits your description perfectly, you should give it a try :3
btw don't mind the horror tag, it's not even a little bit scary. It's mostly a romcom ^^
Introverted boss
Oh my venus
Noble my love
Sensory Couple
Secret garden
Descendants of the sun?
It's ok that's love (i've heard that it doesn't have a love triangle but idk if she's a noona)
The best future
W
@Asena I've never watched Bring it on ghost because of the supernatural element, but if you say it's adorable I'll give it a try, thank you :)

@Lyra I'll try Sensory Couple and The best future, they are the only two,between those you mentioned, that I haven't seen. And I highly recommend to you "It's okay that's love", it's one of my favourite drama! Thank you for your answer!

I don't understand if this is how you respond to an answer... 
I have some here for you even tho it was hard since you've seen most of them :)

Mask - It has some romance, some comedy, but the plot is more thrilling and psychological. There's no love triangle, I think you'll like this.
That Winter, The Wind Blows - It's a melo, but it's romantic and no love triangle
Heartstrings - It's a light-hearted, cute and fluffly music college drama
King2hearts - a must-see korean drama that is good! Has some action, has some rom-com and thriller. It's a rollercoaster ride.
City Hunter - I actually dislike action dramas but this one's great and definitely a must-see drama! My alltime fav
All I would recommend to you, you have already watched, sorry ... but you liked them :p
Goblin

Descendants of the Sun

It's Ok that's Love and Master's Sun

Oh my Venus

W

Drama with no love triangle and has a happy ending. Kinda hard to think of one rigt now. But maybe try:
Healer
Splash Splash Love
Age of youth
Love O2O - it hss a female 2nd lead that pined after the male lead, but she didnt really have a chance. And as much as she wanted to create a rift between the leads, nothing was able to tear them apart
Surgeons
Ode to Joy
Father is Strange

my shy boss
the girl who sees smells  (I can't like female lead but the story is good)
city hall
healer (beautiful story and pure romance)

My type of drama. Take a look at my favorites, all of them, except for Chicago Typewriter fit your description.