Boyfriend getting drinks with other girl?

So my boyfriend is "best friends" with this girl. They've known each other for 4 years (we've been dating for 1) and during the summer of 2015 had a "thing" & they were hooking up. 
She was my manager this winter (small town) so I have a fairly negative view of her as she was lazy and brought all her personal BS into our work space. 
This morning my bf said she texted him and they are going to get a drink in town.. Since it's taco Tuesday at one dive bar he said he's going to ask her if she wants to go there and eat. 
I'm not 21 so I can't go but honestly I don't think I would've been invited anyways.
Thoughts? Am I the only one who would be uncomfortable with this?