Does anybody know of any anime where the main character (or /important/ supporting character) appears happy/lively on the outside but inside he/she's sad/keeping a secret?
It can be ongoing or completed.
and maybe something fairly recent? I've seen naruto, furuba, ouran host club, getbackers..

Try Inu x Boku SS, Rurouni Kenshin, Eureka Seven, Darker than Black, Hakushaku to Yousei, Kaze no Stigma, Nurarihyon no Mago.

That's all I can come up with for now. Hope this helped.

Seen most of them and didn't like most of them, lol.
I'm looking more for happy/lively/outgoing on the outside like Kenshin, rather than blunt/mean like the girl from InuxBoku.
I'll give Nurarihyon no Mago a try though, I see it around a lot..thanks :]

I've got some examples but there's not all main characters :/
I would say Kida Masaomi from Durarara
HunterxHunter (Killua)
Puella Magi Madoka Magica (Homura)
Gintama (Gin)
Angel Beats (Yurippe)
Sola (Matsuri)
Pandora Hearts (Oz)

Eureka Seven, Trinity Blood, Last Exile, Darker Than Black, Black Lagoon, Baccano, Trigun, Gungrave, and Claymore. Those are the ones i can think of off the top of my head hope this helps =)

Try Rahxephon But I have to tell you

It'll have to be watched a few times to understand the plot

Shuffle!... from the top of my head
has a yandere and someone that fits your description
don't want to spoil it though

gonna look for more stuff

Spice and Wolf
Maybe Fruits Basket but I'm not sure about it