Are NF's loyal? IME... No. They are flighty. Never have their priorities straight. For people who are so "people-orientated" a lot of them dont have many close friends.
IME Sp and Sj are far more loyal. Sticking with their true friends when they most need them. NFs are so wrapped up in themselves. I think they are the most selfish people out there. Ever talk to an NF on the phone? Garauntee the conversation will always find a way back to the NF's favorite topic.... themself.
However, NF's are prone to the "holding onto a shitty relationship way too long" syndrome. Could that even be considered loyal? It seems like something else to me. Neediness, clinginess. Not loyalty.
They're also hypocrites. Will leech onto you and depend on you for everything. For emotional stability. For friendship. Will want to share their whole life with you. They want to tell you all their problems. But as soon as you need them for something, it's never as important as when THEY have a problem.
These are the type of people... You could save their life one day. And they next day they would end your friendship because they need to "find themself and start over".