How to get over a friendship betrayal, any advice appreciated

I was best friends with twins, Kayla and Sean. We knew each other since early childhood and now we are well in our 20s as we grew up we merged friend groups and became inseparable. The main group consisted of me, Kayla Sean and Kayla’s boyfriend Alex. We would hang out constantly and go on group trips. It was really a great friend group. We had a few other people join the friend group, including Melvin and Dino.

A few years ago, my best friend‘s boyfriend Alex confessed his love to me. It was a horrible situation where it began with him, expressing his unhappiness with her and how they are no longer working out and that he is happier with me. He tried showing me proof. The proof was pictures of him sad with her and smiling with me. I shut this down really quickly, and after a few hours, decided to tell Kayla that was when I received threats from him. Alex was with her and overheard me trying to explain the situation. He threatened me. He messaged me that if I ever said anything to her, I will regret it. He blackmailed me. He threatened to expose pictures of me where I was drinking and smoking. He claimed he will show them to my family as well as send them out to perspective schools that I was applying to. He said the most vile things to me and would harass me from different phone numbers after I blocked him. He tried to turn everyone against me and claimed that I came onto to him. My whole world turned upside down in a matter of days and I was having a really difficult time. Kayla at first didn’t believe me but the details of their sex life that he shared with me was proof that the conversation did occur. They broke up, but eventually got back together and now my friendship with her is not the same as I refuse to have anything to do with him and she is claiming that it was a big misunderstanding. We went from talking every day to texting once a month. Sean, her twin brother didn’t believe anything Alex had to say. He claimed that Alex had a big ego and nothing can be done. He told Alex that he does not want to be part of this argument and did not want to hear any details. But didn’t outwardly defend me or tell him to stop harassing me. Melvin agreed that everything that Alex was doing was horrible and outrageous but also didn’t really stick up for me or pick a side. I never asked anyone to pick aside because I believe that if someone truly wants to they would and I didn’t want to force anything on anyone. At first, I tried to be understanding. I try to see why my friends weren’t just as outraged as I was. Because if the same thing happened to them I would be 100% be on their side and go to war for them, but they couldn’t even tell Alex off. I was devastated. I felt like I lost everyone. I tried to keep the friendships going. I really did, but I slowly began to realize that maybe I had it all wrong. That maybe we weren’t as close as I thought we were. A few months after the argument I slowly stopped talking and two years past.

I got back in touch with Sean and we discussed everything and he apologized and explain to me that he couldn’t just cut off Alex because then he would have full control of his sister. And I somewhat understood his side and we have reconciled. We now talk almost every day but deep down I am still hurt. Melvin on the other hand has no idea that I am upset with him. I have no idea how to start this conversation. I started talking and hanging out with him more often this past few months and something he said, triggered all of this to resurface. We were watching a movie where a woman got kidnapped and he claimed that he would fight for all of us in that situation. I couldn’t help but snort because deep down I am so hurt by the fact that he never stood up for me. He makes it seem that we are such good friends, but I’m terrified to trust him again. And I truly do not want to go through all of that again. everyone I tell the story to is always shocked that I called Melvin a friend. He has a great qualities, but I just have no idea how to even bring up this conversation or if it’s even worth it. Do I talk to him or do I cut him off? It will be very difficult to cut him off and distance myself from him. But I just keep remembering the great times we had and it hurts. The worst part is that he truly took care of me in times where I was vulnerable or hurt. But in reality when it mattered most he just let me get completely broken down by Alex.

Any advice would help.