To address the question directly - yes, it is authenticating your application every time. However, on the scale of standard web-application this time is don't-you-even-worry-about-it miniscule.
Combining those routes into one might well be a good idea not because authentication has to happen multiple times, but because a web request can simply take a while. Typically this is due to the time it takes to physically send signals from the server to the client over TCP/IP (and re-send to compensate for any dropped packets). Even when parallelizing requests, fewer web requests is faster.
That being said, by default I would do the simplest thing possible and not worry about it. What I just mentioned is an optimization, should be treated as such, and not done prematurely.
As for authentication? It's just a few steps of the super-marathon that is your web request, it really doesn't matter. Someone correct me if I'm wrong, but I don't think it usually even hits the database - all it has to do is decode the claims that are stored in a cryptographically-secure fashion in the authentication cookie.