Boyfriend always with other girls

My boyfriend hangs out with many girls. Which is fine. However, most of the time he can’t go on dates and chooses to party or go out to eat with his female friends instead of hanging out with me. He chooses to be with them instead of with me. There’s one girl in particular that he always texts while he’s with me, and he even brings her with him when me and him are supposed to eat or study together, with just the two of it. He didn’t even tell her we were dating, and apparently my best friend had to tell her, even though she would constantly be with me and my boyfriend. He would also only focus on her when he was with us.

I got mad at him for this, and he said he never thought it was a problem because his old girlfriends were really close to guys and even their exes, so he thought it was normal. I know he’s only sexually attracted to me, but sometimes I worry that he’s emotionally cheating/emotionally attached to this other girl. What should I do??