Note that your query does not tell me what table the fields
DBudget and Cost are coming from so I can't be certain of
this.

Check your data in table tblDeliverables.  I'll bet there
are two records with fkProjectID = 3

When you left join a parent table to a child table you get a
record for each matching record in the child table (in this
case 3).  This is fine until you add a left join a child2
table, because you now get a result record for each matching
combination of records in the child and the child2 tables
(i'm betting it's 6).

To get what you want, you need to aggregate the values in
each table before joining them to the project table.  While
this can be done with subqueries, I think it's better to use
three queries.

query SupplierCost:
SELECT fkProjectID,
            Sum(IIf([Received]=True, Cost, 0)) AS Exp,
            Sum(IIf([Received]=False, Cost, 0)) AS Comm
FROM tblSuppliers
GROUP BY fkProjectID

query DeliverablesCost:
SELECT fkProjectID,
            Sum(DBudget) AS DelBudget
FROM tblSuppliers
GROUP BY fkProjectID

Since those queries only return a single record for each
project, you can left join those to the projects table:

SELECT tblProjects.ProjectID,
            tblProjects.ProjectName,
            tblProjects.Leader,
            tblProjects.Objective,
            DeliverablesCost.DelBudget,
            SupplierCost.Exp,
            SupplierCost.Comm
FROM (tblProjects
LEFT JOIN DeliverablesCost
    ON tblProjects.ProjectID =  DeliverablesCost.fkProjectID)
LEFT JOIN SupplierCost
    ON tblProjects.ProjectID = SupplierCost.fkProjectID