Favouritism is unfair but it happens in lots of work situations. The only way to address it is to be assertive. Easier said than done but a skill that lots of people (managers included) could benefit from.
Sometimes it can appear that everyone is being given better opportunities but, we only see it from where were standing. Things change, jobs, people, takeovers, etc so although it can be crappy, knowing that "change is coming" could help how you view it. There are lots of retail shops with good managers so if it doesn't work out perhaps a change is on the cards. Wish you well.