Jim, your claim was based on a reported quote from one "unnamed government source."
Since then Cameron has continued to demand that Assad be removed, as has Obama and all Western leaders.

Your claim, "we are now actively supporting the Syrian mass-murderer and demanding he be left in control of the people he has massacred." is entirely false!

The supporters of Assad are Russia, Iran and China, not the West.

the West's failure to act on Assad's atrocities, and leaving him where he is will only ensure that he continues where he hasn't really left off.
Obama and Cameron wanted to launch reprisal raids against Assad, but the British left defeated the move.
Meanwhile Russia has a huge military presence in Syria.