Tensions within the coalition have been increasing in recent months and the friendly relationship evident in the Number 10 Rose Garden back in May 2010 seems like a life time away.
There have been a couple of good articles looking at the tensions in the coalition over recent months.
This piece in the Telegraph is looking at the clear divide between the Conservatives and Liberals over trident. This division dates back to 2010. http://www.telegraph.co.uk/news/uknews/scotland/9641757/Coalition-splits-allow-SNP-to-wriggle-off-the-hook.html
This piece is broader, it looks at the divisions over schools, health and banking
And finally the perennial question of Europe.