Around the time these photos were taken, Yamano Yuri was dating Kanjani8's Murakami Shingo and that apparently, Aiba stole Yamano from him. She even broke up with Murakami via text, simply saying “We’re (Aiba and I) in a good place right now. Don’t call me.”[a]
However when the time came when it was their relationship's turn to end, Yuri posted the above photos online, obviously not happy with the break up. As for Aiba, he was almost kicked out of Arashi when the pictures leaked out. Thanks to the ever loyal fanbase, Aiba was allowed to stay. If he were a junior when all of this took place, there would be no Arashi sunshine on screen today.
UPDATE 8/19/2013: Got hold of more Yamano Yuri x Aiba Masaki pics! Here they are:
2007 Asami Mizukawa
A February issue of FRIDAY 'exposed' Aiba Masaki and Mizukawa's supposed relationship. According to them, Mizukawa and Aiba started dating in 2007. but they broke up in the fall of 2008 because of their busy careers. However, they got back together about a year later. Late Junuary of 2012, with a mask, Mizukawa was spotted at Aiba's apartment building. She was also seen visiting twice during the later part of 2009. 
During a Press conference for the stage play Kimi to Miru Sen no Yume Masaki Aiba denied any romantic relationship with Mizukawa Asami, stating “We're not dating. We are just friends,”  Maybe hoping to make the public believe it.Currently, rumors persist that they are somehow still together.