Drama/relationships

So I’m best friends with this boy. At the beginning of the year he got a girlfriend and she’s kinda tore us apart. Me and my best friend now fight all the time and end up blocking eachother. Last night I had a great talk with him because I found his number. But he told his girlfriend about the talk and she texted me and started going off on me and blaming me for things that never happened. Saying things like I made him cheat on her and things like that. When me and him talked all we did was tell eachother that we miss our old relationship and played 8 ball😂. Now I can’t be friends with him anymore because of his girlfriend. How do I get him out of that situation? I know he wants to be friends with me and I know he’s miserable in his relationship, but he can’t let go.