Forbidden love/infidelity/Moving on

So I met this in an app and we became friends. After a few months, we ended up dating. The situation is, she is has a boyfriend and been together for 7 years. I guess what pushes her to do this was she bot getting the attention and love she needs? She mentioned that they are like friends. Not doing romantic stuff. And caught the guy asking women for nudes. We got along well, she always says how I made her very happy. I gave her all the love I could give and things I think can make her happy. At first, I was thinking of breaking up cause I know in the end, I'll get hurt. I told her she doesn't need me, her bf can give what I can and she said I was different. So we stayed together. Then I kept bugging her about it and she got pissed and I said okay, I'll stop talking about it. She always says that she doesn't think she and the guy would split, that we are going nowhere. 2 years had passed. We were very happy and I was planning to visit Colorado. Then I don't know what happened to me but I feel shit most of the time and asked her what if he proposed, she said she doubt it would. What are you going to do? What will happen to us? She doesn't know. She doesn't wanna answer, she doesn't have an answer. A month after the guy proposed and she dumped me. It was 4 months ago. I still struggle af. It hurts me deeply though I know partly it's my fault. We both don't wanna cease the communication but I am afraid that she will forget me. We still talk every day like we used to but not romantic anymore. She wants us to stay friends and communicate. She's trying to be 100 and be there for me as she says. The love I have for her is different than my previous relationships, I always needed her. I don't know what to do. I am losing my mind. Why do I feel like she doesn't care? That she isn't going through the same struggle as I do? Like everything was so easy for her like it's not even affecting her.