Regardless if this was right or wrong for them to talk daily, I still think you had to take it up with him, not her. If he is talking too much to other girl then it’s something to address with him. Just because other girls contact him or he is assessible, doesn’t mean he needs to respond every time. If he felt it’s too much, he should have stopped. He is an adult.

In the future if you see your partner is doing something with the other woman that makes you uncomfortable, you bring it up with him, not other women. Frankly daily contact with someone your girlfriend introduced you to is excessive. Even though I said my husband talks to many different people, I can’t imagine him contacting my girlfriend daily (and vice versa) , especially if he didn’t even know her prior to meeting me. It’s bizarre.