It seems like you are running SQL Server together with an application on one server.
SQL Server will consume all the memory it can by design. (The default MAX memory setting in SQL Server being 2147483647 MB.)
If you changed the default MAX memory setting to something else, then SQL Server will start consuming memory after a reboot for data cache, query plan cache, and for other SQL Server relevant components.
At some point in time the SQL Server will pass the MIN memory setting. SQL Server will not release memory back to the OS past this setting.
Later on the SQL Server instance will possibly reach the MAX memory setting. SQL Server will not pass this line for data cache and plan cache. However, the SQL Server process can use more than the MAX memory server setting, because some objects run outside of the MAX memory setting (depending on version) and SQL Server can overcommit memory. This is discussed in the following article
Memory configuration and sizing considerations in SQL Server 2012 and later versions
Your SQL Server will now consume memory between the MIN and MAX memory setting until you reboot the SQL Server instance.
CAUTION: Reducing the MAX memory setting of a running SQL Server instance will purge the data cache in memory and result in a reduction in performance.
If your SQL Server instance is running on an application server and not on its own, then you might have to reduce the MAX memory setting for SQL Server to allow the application to have some share of the memory.
If your SQL Server instance is running on its own, then try configuring the MAX memory setting according to the following recommendation:
...reserve 1 GB of RAM for the OS, 1 GB for each 4 GB of RAM installed from 4–16 GB, and then 1 GB for every 8 GB RAM installed above 16 GB RAM...
Reference: How much memory does my SQL Server actually need? (SQLSkills.com)
There are some other good articles out their that explain how SQL Server uses RAM.