Partner talking to old FWB

I am in the best relationship I’ve ever experience. I’ve been with her for almost a year now and we are best friends. We have been very open with each other from the beginning and we both put effort into the relationship and into working through issues together. We both were in bad relationships before we met each other and we both have the same desires in this relationship. We both have left over issues from our past though as does everyone. We are living together and are raising our three kids together now, my two and her one. I work away from home for three weeks at a time, a long way from home.

She kicked her sons dad out a couple years ago when the emotional abuse turned toward physical abuse. Shortly afterward she started talking to an old high school friend. That turned into an FWB thing as she wasn’t ready for anything serious. That went on for a few months. About a year later we met, at that point she was interested in something serious, but wasn’t interested in the FWB in that way. We began dating and are a very happy couple now. She was not seeing the FWB anymore when we started dating. But she made me aware of him and he was still a friend. They however didn’t really speak much or see eachother. Last winter there was an event in which my partner needed to help her mother find an apartment. She called the FWB for advice on a land lord to call, which she told me about. I didn’t have any issue with that. When I got home from work though I got curious and I invaded her privacy by looking at her phone. It was a crappy move and I’m not proud of it. Anyway, they had begun talking a little. She told him about me and was clear that she was with me. But she had said she might come by for a drink sometime to unwind. He made a joke saying “okay but not like we used to, winky face” referring to the extra part of their old relationship. That pissed me off and I didn’t appreciate him flirting or joking about that part of their past. I admitted to the snooping and we discussed it in detail. We discussed comfort zone in being friends with people of that nature and I explained that having a drink with him at his house would be beyond my comfort zone. She understood and actually quit talking to him even though I didn’t ask for that. I did however ask that she tell me if they started talking again, she agreed.
Flash forward to now. There was some tragedy in her family. The FWB contacted her with sincere concern, as any real friend would do. They started texting again here and there, but she wasn’t comfortable with telling me, probably due to my stupid actions with the snooping. Anyway a few days ago we were running errands and her phone was getting blown up and she was acting way out of character about it. Very private and secretive about it. I got suspicious and looked when a text came in and it was his number. That’s how I found out. So that night I asked her if someone was texting her that she felt uncomfortable with me knowing about and she denied it. So I point blank told her I knew the FWB was texting her and I felt threatened by the secrecy. She insisted I read the text and even though I didn’t want to invade her privacy again I did because she wanted me to. Low and behold they were just catching up and she spent most of the conversation talking about me and how happy she was. She said if it made me uncomfortable she wouldnt be friends with him. I told her that’s not what I wanted for her and its not what I wanted for our relationship. I just want things like that to be out in the open and I want to feel secure in that boundaries went crossed by him.
I have a jealous streak, but I am aware of it and I don’t let it control me or my relationship with her. I want to work past it so we don’t have that in our relationship and I don’t think limiting her on who she can be friends with is healthy or productive in dealing with my jealousy issue and I wouldn’t feel good about myself if she had to choose me over friends.
My questions
Did I make the right choice in encouraging her friendship with him even though for the time being it causes me fear and pain? Should I have taken her up on her offer to not talk to him?
How can I deal with this and stay sane until I can become comfortable with that friendship?
Should I feel threatened by her wanting to talk to and be friends with someone she had a physical relationship with?

Thank you for reading this and thank you in advance for your thoughts.