I've become a stalwart fan of the local Starbucks Reserve here.

[Silverobama]

In my neighborhood in the newly opened shopping mall, there's a Starbucks Reserve. It's the only one in my district (place I live) and one of the five ones in my city. I like the environment there and I like the people there. I become gradually fond of it. Is my italic sentence natural to describe this feeling "I've become a stalwart fan of the local Starbucks Reserve here".

[teechar]

In my neighborhood in the newly opened shopping mall in my neighborhood, there's a Starbucks Reserve. It's the only one in my district (place I live) and one of the five ones in my city. I like the environment there and I like the people there. I become gradually fond of it. Is my italic sentence natural to describe this feeling? "I've become a stalwart fan of the local Starbucks Reserve here".

It's possible, but I would likely use "avid" or "keen" instead of "stalwart" which I think is too strong for that context. Also, "here" is unnecessary.

[tedmc]

Stalwart does not go with fan since the former also means a fan or supporter.

[Silverobama]

I've become an avid/keen fan of the local Starbucks Reserve.
I've become an avid/keen fan of the Starbucks Reserve here.

Are they both okay natural now?

[teechar]

I prefer the one without "here".