Male lead likes his childood/best friend, the female lead, but she likes another guy. In the end though, she realizes she likes the male lead as well. Would be nice if there are misunderstandings, but not required.

Here are some manga which fits your request (or at least somewhat). They are rated based on the RELEVANCE to this request.

Super Secret (5/5, or at least it might be heading that way...)
Ongoing webtoon, which you can read at http://webtoons.com/en/. About a girl who's actually living with supernatural beings. She has a boyfriend, but there is this childhood friend who likes her, too (she doesn't know that though). It's not clear about whom she will end up with, but the childhood friend has a good chance of winning, I think!
Sakurasaku Shoukougun (5/5)
Completed. Definitely fits this. About a delinquent girl who likes a guy, but her childhood friend also likes her. A bit dramatic if I remember correctly - I read this manga around 1-2 years ago.
Teruteru x Shounen (4/5)
Completed. About a boy who becomes a ninja to protect the girl he likes. I think the girl has a crush on her guardian (at first), but it's clear that she gradually falls in love with her childhood friend, too. Very sweet romance <3.
Uwasa no Midori-kun!! (4/5)
Ongoing scanlation. About a girl who wants to master soccer to defeat a childhood friend who did something terrible to her in the past, so she enrolls in an all-boys school. There's also a guy at her school who likes her. I have no idea who she will end up with though, since I have not finished reading this.

The manga above fit your request, but here are some other manga that "somewhat" fits:

Koisuru Harinezumi, but the childhood friend (who's also the male lead's ex-girlfriend) is only an obstacle in the male lead x female lead's relationship, so their love triangle doesn't last very long (and is only minor in my opinion). The main couple are not childhood friends.

You can also try Beauty Pop if you want. There's a love triangle going on (warning: romance is not the main plot in the manga), and one of the male leads met the girl when they were still children - but I'm not sure if you'd call them childhood friends haha. But the childhood friend is not really an important part in the story.

Or, how about Suki Desu Suzuki-kun!!? The main couple is not childhood friends, but the guy has a female childhood friend. And there's also another guy who likes the main guy's childhood friend. So it's like: Main Girl -> <- Main Guy <- Childhood friend <- Guy 2. The main story revolves around Main Girl and Main Guy. Childhood Friend and Guy 2 is a side pairing.

(And I heard that Nisekoi and Taiyou no Ie fits your request, so you might want to take a look at them.)

Oh, if you're also interested, here are some romance manga between childhood friends (not sure if there are love triangles though):

• Ookami Nanka Kowaikunai!?
• Last Game (Has a love triangle I heard, but it's kind of obvious who the female lead will end up with. Oh, and the main couple is already childhood friends.)
• Max Lovely!
• Kiss made no Kyori (YOSHINAGA Yuu)
• Dear Mine (somewhat; Male lead meets female lead when he was still a child, and he still loves her after all this time.)

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