My friend is dating a manipulative psychopath

I asked my good friend why he blocked me on instagram, and he said it is because of his new girlfriend (whom he dated about 9 months ago but recently got back together with). He then showed me he isn't following any girls on any social media, even his own girlfriend because she won't let him follow her (I presume she has something to hide). When they dated in the past she cheated on him 4 times, she knows all of his passwords but he doesn't know hers, she got him addicted to pills (adderal, xanax, etc), she destroyed all of his friendships, and she demands he buy her expensive gifts. His parents cannot stand her. He recently maxed out his credit card buying her the ENTIRE Pandora Rosegold Collection. He will not listen to me when I say she is toxic. What should I tell him? The hardest part about watching this for me is that while he is currently my friend, he is also my ex boyfriend and even though things didn't work out between us romantically I still care so much about him. I told him, "I don't care who you put your dick in, just not her".