Just taking it off my chest

I dont know where to start. Its gonna be a long post.

I am an introvert. Dont talk to people if I am not comfortable with them. So most of the time, I am just keeping on my own, at work and home. 4 months ago, this girl at my work place, she started to have a little chat with me. First she started with something related to work. One day she was working with me and I was playing a game on mobile. I showed her the game and we started playing the game. We started playing this game every day even late night. We were also having chat on this game. Then we started having chat on other social media apps. She started telling me about her life and everything. I started telling her everything too. She got a BF and she was having a bad time in her relationship. One Night he didn't come to her whilst she was struggling. She was playing this game with me and started telling me that she is not well and having mental breakdown. And then told me her BF didn't come. So I was there talking to her till she was ok. Then she started to open up more and more. Telling me everything what he says and what he do. We started to have late night chats and talking to each other for hours. Then one day he said He doesn't wanna continue this relationship and she was crying her eyes out. I was there to calm her. I stayed on video call until she was ok and went to sleep. Next day, they had argument but then things settled down. Her BF knew she have a friend and he started giving her shit about me. But she was on my side, saying she is not gonna leave me for him. In mean time she started telling me how she feels about me. She even said that she feels more seual attraction towards me than him. Everything was ok until I was going away for couple of weeks. Before I was going away, I came to know that she had sx with him. I started crying as I thought she was not into him. But she said she is still in relationship and its not a big deal and things are still the same with him. But for me its was too much. I was heartbroken. After that, I was not able to be the same. And she was trying to be distant. Now, she stopped telling me anything about her life. I tried to ask if everything ok and why she is not telling me but she said she doesn't need to tell me everything. I feel like she is trying to distant her self now as things are ok with her boyfriend. But I dont know what to do, she still wants me as a best friend but she doesn't share anything with me, doesn't talk unless I initiate. She is not the same person anymore.

I am going no contact. Just saying Hi at work or something related to work only. Trying my best to not think about her. Its hard to do something that you dont wanna do.