My bestfriend's husband threatens me

So my best friend was here over the weekend to take some time off from stress with work and her husband's drama she flew in from HI to NV last thursday, and we already had a plan to go to Universal Studios and so we did she paid for our plane ticket, airbnb and we half for the rest of the expenses needed for the trip, we meet up with our good friends, they took us to see santa monica pier and had dinner and then we left, we stayed there for 2 nights and 3 days.

I had a great time both of us it was a very short trip but we forgot our stress for sometime and we get to bond with each other again, monday was technically her last day because she's flying back home on Tuesday midnight, I have school on Monday and i'm in night class, as soon as I got off school, I pick her up and we drove to see one of our good friends before we head to the airport and so we did we were talking stories and then i finally dropped her off, as I was driving back i received a call from her messenger and so I thought maybe she forgot something so I answered it and it was her abusive husband, right away he was cussing at me calling me names and harrasing me he was telling me that I am a bad influence to her and that I would hook her up to guys so that both of us can have sex with different men.

He was talking about a post from one of our friend and accusing me that our guy friend and her wife was in a hotel bed, i told him to send the photo and it was clearly bright as the sun that it was not her, like literally not my best friend but he was insisting that it was her, and so he was threatening me that he will come here next week and hurt me and also tell my husband that I am cheating (which is we all both know I am not) he was also accusing me that I am ruining their relationship, which is not true.

Her husband's background:

So he has been cheating for like 4 years, he has a girlfriend in person and they live together they recently got an apartment, he also tells me that they are both over each other, she just lets him do what he wants because she doesn't love him anymore but they have 2 daughters, and married he would always tell her that if you filed for a divorce I will take the kids away and kill you and your family, basically, he gets away with all his trouble because she lets him do it and she doesn't want anymore trouble, but when it comes to her he is not allowing her to talk to other guys even if its just a friendly talk because she is ready to date also but he always hacks her accounts and threatens them and me for some reason.

He also had another girlfriend besides the one that he is currently living with but she's in the philippines and he let her live with his mom.

So, last night i was so mad driving home and i message her before she board her flight and she just tells me to live him alone to not reply and just ignore him, he has been doing this to me everytime he finds out that she's talking to other guys, now i don't know what to do, i would like to file a TRO case against him or something because he won't stop threatening me. I understand that she is really afraid of him but I dont understand why she would not make a legal action against him and his girlfriend, i tried talking to her about it but she would just listen but she doesn't respond to any of my advice.