I found out my now ex boyfriend has a fiancé and he is manipulating my friends

I have known this guy for a year and at first it was only sexual but we always used to go on dates and hang out. Eventually, we become offical and he has always been controlling whenever I went out, requesting for me to keep my location on. But he was always affectionate and attentive. He would always make the effort and we would go on a few getaway. From the beginning of our relo, I always had doubts and red flags about it but never pushed for it or listened to my instincts that he was lying or cheating. I’ve known him for a year yet every time I request to meet his parents he would come up with an excuse saying that we weren’t offical yet or purely because I didn’t want to him them. Yes, it is true I didn’t want to meet them as we weren’t offical in the beginning but I did ask to meet them. He’s interacted with my entire family as every week we would have family dinner and he would with my every day for the last 7 months but I still haven’t met his close friends which was always a concern that I raised.
Throughout, our relo we did break up 2 times however he would always beg me to give him another chance and blamed it on that I was scared to see a future with him.
Fast forward, last month we officially broke up after a car accident. A car accident that he deliberately cause after we broke up, I broke up with him in the car after he yanked my phone out of my hand and accused me of cheating. At one stage he took off my seatbelt and tried pushing me out of a moving car.
After the break up, I was devastated but then found out that he was always engage and they have been together for the last 10 years. When I confronted him, he explained that he did love me and he did fall in love with me which caught him off guard however, I doubted him that he would’ve choose me even when he said he was having a hard time and wanted to confess. But he was scared that he would’ve lost me and her (his safety net)

We barely are on speaking term now. I plan on doing the No contact rule for 1 month but it’s hard.
I found out from my friends that he has been trying to manipulate them to give a different perspective of the car accident (he said I caused it) and of me. He managed to get in between one of my friends as he now feels the trust is gone.
Part of my knows that they know then they let on. Even though, they tell me they don’t like them

What should I do! Help me! I know this group “my boy groups” are hesitant and does not fully have my back. But why do I care about them or my ex?