[M20] and my ex who is [F19] how do I get over the hurt of my ex leading me on then getting a new boyfriend?

I was with my ex girlfriend for 2 years we broke up a year ago. We took a 2 week break after the break up ever since talked on FaceTime 5+ hours per day. Recently my ex called me up, with watery eyes, stayed silent for 10 minutes i was confused because usually we call laugh and have a great time every night talking about our day and things. No this night was different. She admitted to being in a relationship for a week now. This was confusing to me because why was she crying so loudly after she said that, and why did she care so much to tell me, and why did she not tell me for an entire week but act like everything was normal. I was of course sad because Ex’s don’t call 5 hours per day text for 2 hours, and share everything about their lives not even best friends do, but I guess that’s what it was. She would casually flirt with me calling me daddy, and I’d call her mommy she shared all her private things about her wanting an apartment private things about her parents geez she must trust me to say this.

About a week 1/2 ago we met up and hung out for 7 hours it went great she and I were naturally having a good time and meshing. But that struck me because she had a boyfriend but hung out with her ex boyfriend for 7 hours, and talked to me for 3 hours after that when I was riding back. She called me last night to when we were calling she was tearing up yet again, and fell asleep on call with me coddled in her blanket. (Don’t you do this with your boyfriend not me?) what the hell is going on I thought. She’s spending more time with me than her bf. It’s like she’s using both of us when one isn’t available the other is. I told her on call we can’t be best friends, she begged for me to please remain her best friend. I told her the feelings weren’t mutual, I’m happy for you, but I can’t talk to you while you have a boyfriend, you chose what you chose, and I don’t agree with that I care about you, but it will only cause arguments as we spent so much time together so many memories and now you want, that with someone else and me when I don’t feel that way it just wouldn’t work. After guilting me into calling her again tonight I agreed to, she seems better less sad, but how do I finally tell her I’m not her fiddle, I am the first option not #2. Even when I still love her but can’t pursue. Why does she spend more time with me than her boyfriend? I think she feels pity and guilt because she knew I had feelings for her. And she does too and doesn’t want me to leave but is trying something new even if she doesn’t want to fully move on and I can’t be apart of it no not on my standards.

TL;DR ex got a boyfriend but is still pretending like we’re dating how the hell do I tel her I’m not interested if you have a boyfriend because I feel more, and she keeps guilting me into staying.