This was terrible advice. You don't dump your friends for a new girlfriend, and you don't especially dump your friends when the new person demands it. 

At least one of you should have said 'well, maybe you could meet his girlfriend and talk to her about it.' Buuut no. You instead went 'WELP. NEW GIRLFRIEND WINS. Friendship over. Get over it."  This is terrible advice. This is -TERRIBLE- advice! Control of outside contacts is the first thing an abusive person does in a relationship. I'm not saying that his girlfriend is an abusive person, but you don't know if she is or not. Her behavior is controlling. That is not good for anyone.

Good advice would have been. " Hey, extend the olive branch. Talk to his new girlfriend. Alleviate her worries and try to make friends with her. If she refuses, then she's obviously not interested in compromising on anything with her new beau. Talk to your friend afterwards."    Good lord, you two.