Oftentimes "loyalty" is defined by (our) "expectations" and the circumstances.
There may be an instance where someone is down on their luck and their friend offers to pay for their meal or drinks or even spot them some cash. Most people would consider that the act of a loyal friend.
On the other hand if he later told another person how broke their friend is then he/she might be considered "disloyal" in the eyes of some folks even if the friend didn't ask for it to be kept a "secret".
Truth be told in a lot of instances the so called "disloyal friend" does not see them self as being disloyal at all. It's up to us to gage the personality of our friends before deciding what to trust them with.
It's unrealistic to expect someone to be anything other than them self!
Over time you get to observe their nature. Each of us chooses our own friends, lovers, and spouse. If someone is having problems finding loyal friends they need to re-examine their "friend selection" criteria as well as their expectations.
Define your friendships: best friends, friends, and acquaintances.