<human>: My girlfriend and I recently moved to a new city. We started going to a gym here and meeting new people.

There's a guy at the gym she met, and they have become friends. Recently, they've taken their friendship outside the gym -- he asked her to join him for drinks, I only knew that she went because she texted me that she was going to see him before she left. 

It's a couple days later now, and he's asked her if she wants to grab dinner with him on Friday. They also text constantly to each other.

There are a zillion red flags and warning bells going off on my head about this. I have no reason to believe my girlfriend would ever cheat on me (she's very affectionate and spends lots of time with me), but I feel like I have a huge pit in my stomach over this. 

Am I being insecure about this? Or should I be worried that this "friend" has basically started asking her out on dates and she's going along with it -- regardless of whether or not she feels her friendship with him is purely platonic (she's told me it is but I believe his intentions are different).

I'd just come straight out and tell her how I feel, but I'm not sure if doing so would make me look like a control freak, or if my concerns here are legitimate.

Is it unreasonable for me to expect exclusivity with my partner, when it comes to hanging out one-on-one with a member of the opposite sex?

Could you distill the essence of the text into 1-3 sentences?
<bot>: girlfriend spending one-on-one time with a new guy friend she met at the gym, and texting him constantly. I'm worried. Should I be?