Reading about WWII and Italy's involvement it seems to be a failed offensive after failed offensive... Greece, Egypt, etc. Did Mussolini force the Axis forced to spread themselves too thin and did this have a great effect on Germany losing the war?
Not really, a common arguments is that hitler's forced intervention in Greece delayed Barbarossa and caused Germany to be caught in winter and not be able to take Moscow. This is false, because Barbarossa was going to be delayed anyway because the Soviet Union was still recovering from the rainy season and the roads were all drowned in mud.
The German intervention in Africa was costly for the Germans, but it didn't cost the Germans the war. The Italian collapse did do a lot of damage to the Germans, as they forced to take over the Italian occupied areas and they forced the Germans to send significant amount of men and resources to defend their southern flank. It also pulled the Germans first into a two front war and later a three front war.
So while it's not correct to say the Italians cost the Germans the war, the Italians did hamper the German war effort.
Sources:
The Second World War : John Keegan The third reich at war