Breakups

A month ago today my boyfriend of 9 months broke up with me after we were in a pretty serious relationship, looking for our own place and stuff. Now he has a new girlfriend, who for the first few weeks of the breakup was actually the person saying they were trying to get us back together. My ex and I are still close we talk pretty much everyday about everything but I asked him to not mention her. How do I keep my best friend when his new girlfriend has done so much to torment me ( more to the story I don’t really wanna post)