Looking for some yaoi where one boy falls in love with his sibling's best friend or vice-versa.
I think i've read some but i can't remember.
I also prefer them to be completed
It can also be an online fiction if you can't think of any manga

Empty heart is sort of what you want. The main character actually likes his best friend but end up with the sibling.

Bucchou Baby by Shiuko Kano - Though it's not really scanlated and the **cough, cough** scans I've seen are pretty bad.

Vibration Life by S-Kun, but it's not complete nor does it look like it'll be completed any time soon either. However, I recommend it because has so much potential and the art is great. I hope she comes back to this manhwa someday.

In case you didn't notice it, this thread is extremely similar
[http://www.mangaupdates.com/showtopic.php?tid=39730]
In that thread I posted a link to a previous thread with other suggestions.

only one that comes to mind is Boku wa Kimi no Tori ni Naritai-- a guy falls for his big sisters boyfriend

also vibration life is just a stupid suggestion- its not being scanlated and it doesnt look like it will be any time in the near future. why would anybody want to start reading something that they can never finish.

First of all, I believed I mentioned in my post that it was an incomplete manga, thank you for the newsflash Captain Obvious. I suggested it because I felt the story was worth reading despite its unfinished status. I knew going into it that there was a possibility of it never being completed and I still read it. It's four measly chapters long, what does anyone have to lose in reading just four chapters?