I'm not sure. If he seems hesitant to let his gf meet up with you... that is a red flag. But if he is okay about it... I guess it should be okay to meet up in a casual surrounding.
Thank you! I think he didn't hesitant, he just asked me if I want to meet his friends. And I took the chance to set the boundaries, lol. It seems he is sensitive about it at one moment, and callous the next.