I am not sure why you asked her to stop talking to him if he is the one you are dating? He was the one you had to talk to about excessive communications with other girl.

But if you two weren’t really dating, you just “liked” him then he and the girl are free to talk to whoever.

Overall it’s really depends on the context and specifics, I just don’t know enough to make a judgment what’s right what’s wrong as you didn’t explain enough. My husband talks to all kind of people and I can’t care less. Not like he is talking while on a date with me or being inappropriate or flirty. I am not threatened by him simply talking to people. So I am not sure about your situation