Hitler and Mussolini actually barely tolerated each other. On a personal level, they deeply disliked each other and on a political level there was a great deal of mutual distrust.

Mussolini did not trust Hitler and in the early days of the Nazi regime was a strong defender of Austrian independence as he feared that Anschluss would have meant German demands for former Austrian territory Italy had gained during the First World War. Hitler barely tolerated the very frosty and evasive responses Mussolini gave every time there was an offer of alliance.

Likewise, many in the Italian regime did not particularly like the Germans and abhorred the racial policies enacted. On the other hand, many in the Nazi regime did not have a particularly high opinion of the Italians and only sought an alliance out of necessity.

Even throughout the war, the relationship was very poor. It didn't start particularly well as the Nazi regime had given assurance to Italy that war would not come before 1941 or 1942. So when it came only months after the signing of the Pact of Steel, when the Italian armed forces were woefully unprepared, there was a sense of betrayal and quite a lot of reaentment. And because of their low opinion of the Italians, the Nazis did not entrust particularly sensitive actions to the Italians.

Unfortunately, I'm afraid that the oft repeated story that Hitler and Mussolini were very close and strong allies is simply not true.