I didn't know my son belonged to my best friends husband

Hi Reddit, I'm a long time lurker here and this is my first time ever posting. Im wriring here for advice i guess sorry if its a long post. Im 26F amd I have a son 4M. My best friend since primary school is 26F. She and I are part of a friend group of 5 females. I have never really vibed with my best friends husband, he was always opinionated & rude. All in our mid to late 20s. To start off im a single mother. 5 years ago I was at a Halloween party where I dressed up in as a Ravenclaw & my BFF dressed up in Gryffindor. We're both are die hard Harry Potter fans. Backstory - While we were at the party i got blacked out drunk and all I remember is that I slept with a guy in the bathroom and the light wasnt working as thats what the host told us. I didnt think much of it cause why not I was 21 and my then boyfriend cheated on me. 2 months later I found out I was pregnant, I was scared cause I was a single mother. My BFF was immediately by my side every step of the way and was more excited than I. I decided to keep it cause ngl I think I needed love in my life. Our friends also stepped up and help which I was greatful for. Now onto the story. 2 months ago, my best friend started pulling away slowly distancing herself from me and my son, I didnt think much of it as she & her husband 27M have a 4 week old at the time. I still came by dropping off food for her and her husband as thats what they did to me and I wanted to show my friend that I care & love her as much as she does me. Then about 2 weeks after that she confronted me about my son during our friend weekly get together placing a DNA test result sheet on the table. The probability of my son & her husband were 99.99%. I asked her if this was a joke to which she started yelling at me, she then stopped herself and asked me calmly if I slept with her husband. I told her no that I wouldnt even dream of hurting her that way or is anyway. As shes my sister is all but blood. Note to add Hes cheated on her before but they decided to work on their marraige. Theyve been married for 2 years. I gave her my phone and pointed to my Ipad and told her to go through everything becuase I wouldnt dare do anything like this. I encouraged her to do so, becuase i honestly love all my friends theyre all family to me and my son. She and 2 other friends searched through everything and i watched with the other one sitting beside me. When she didnt find anything. She told me that she'd done not one, not two but 3 tests of my son & her husband. I was shocked grabbing the paper on the table reading it. Swearing up & down to my parents graves that i never slept or even looked at her husband like that. She broke down sobbing that she cant believe this is happening to her. I tried to confort her but our mutual friend 27F told me its best for me to leave for now. I agreed becuase i havent seen my friend this upset in a long time. I told her I loved her and that I'm sorry for her pain. My other friend 24F drove me home while I sobbed. Replaying that night in my head. I hadn't seen the guys face in the dark or heard him as the music was loud and there wasn't a lot of talking. Ive tried reaching out to my best friend but she has blocked me on everything. Our mutal friends were torn so for her sake I told them to go to her as I didnt PPD. Its been weeks since ive heard from her. My friends still do come and check on me and tell me they believe me as said friend's husband have tried making a move on them in the past and havent told our friend this. Now I feel sad and violated and angry. Any advice is needed. PS - sorry if my grammar isn't correct I'm writing from my phone.