Best friends are supposed to be there for each other and not ditch them for other people and so it cannot be fine when it happens.
Consider the statement "My best friend have recently been spending a lot of time with some people from her work.". Based on this "It's no big deal and absolutely fine when my best friend suddenly becomes busy with other people from her work and doesn't have any time for me." a true statement? Yes, no, or I don't know?