To view database roles assigned to users, you can use sys.database_role_members
The following query returns the members of the database roles.
SELECT DP1.name AS DatabaseRoleName,
isnull (DP2.name, 'No members') AS DatabaseUserName
FROM sys.database_role_members AS DRM
RIGHT OUTER JOIN sys.database_principals AS DP1
ON DRM.role_principal_id = DP1.principal_id
LEFT OUTER JOIN sys.database_principals AS DP2
ON DRM.member_principal_id = DP2.principal_id
WHERE DP1.type = 'R'
ORDER BY DP1.name;