So like the subject title says. Is there anything like this?

Main character can be male or female, I don't care. Same goes for the best friend and the love interest. And the one with the sibling can be the protagonist too... so like in 50 Rules for Teenagers where Mi-Roo likes her twin brother's friend.

If there's an age gap, and the younger one is still in high school, they should be absolute maximum five years apart. I get at least mildly creeped out by pairings with a high school girl and a guy that's like 25. Or even younger than 25, really. I don't know. It depends on the execution but I always can't help thinking... What kind of self-respecting university student dates a high school kid? Hm. I think I usually care less about older female x younger male pairing age gaps though.

I don't mind shounen-ai or shoujo-ai but I don't read yaoi/yuri. Also preferably no ecchi, but if it's light and not distracting to the plot then whatever.

Thanks in advance. Feels like I wrote too much...

[url]http://https://www.youtube.com/watch?v=GBRTmeLly1U[/url]

Now that that's out of the way I can answer your question. Although that link could count as #1.

Here I thought I would have a bajillion suggestions for you but I've come up pretty short. Maybe it's less common in manga than Western stuff.

Reborn! Well not best friend.
Card Captor Sakura (Sort of if you know what I mean)

Gosh is that all I could come up with? Manga you disappoint.

@Sapphiresky Hahaha. And thanks for replying. But I've read CCS. And I guess I should have mentioned this before, but I'd like it if the romance was at least a significant subplot.

Is there really nothing else that fits??

Have you tried looking at the In Love with Family Member's Friend tag? (If you think about it, it fits. Like if the male lead was in love with his sister's friend). (sorry too lazy to put a link atm.)
(Edit O.O I can't believe I wrote he's instead of his. I knew it felt wrong, but I was out of it, and didn't think about it too much).

I know one manga where this girl was in love with her older brother's best friend, but I can't remember the name... (I'll edit this when I do remember).

-Sidenote; Oh hey look my 500th post. In the same section as my 1st post was made how nice.

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I'm sure there are a lot more of them but I typically read action/shounen/seinen and not so much romance manga.

I think Mon Seul would be perfect for you. 🤣

Hahaha, now seriously, if you try this, it is one awesome manga. It made me rage, it's sad as hell, sometimes disgusting, but it's absolutely worth the read. Until I read it I didn't believe such hard story could be written so well.

Other manga loosely about siblings issues 😎 would be Haruwaka and then Hitsuji no Namida.

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The only one that I remember right now is Kono Koi wo Wasurenai. third story named the the flower that blooms in you. Its one of my favorite.

Kiss made no Kyori (YOSHINAGA Yuu)- the girl falls in love with her twin brother's best friend