I am having this problem as well. I have a SQL Server 2008 R2 SP2 STD on 16 GB memory and Win 2008 R2 64 BIT, at the beginning, the Memory Manager -> Database Memory takes most of the SQL used memory, but the Memory Manager -> Connection Memory counter keeps increasing until it consumes almost all memory after about a week. I have to restart SQL server to release the memory used by Connection Memory.

When I cut the connections by websense accounts, the memory was release right away. So for now I set a job to cut the websense connections each sunday.