I can't breathe and I don't know what to think.

I (23M) had been talking to this girl (22F) for about 8 months. It was a bit off at times since I pushed her away due to not knowing what she wanted. Until I just decided to be upfront and ask her what intentions she had. She said she liked me but wanted to take it slow, so we did.

Everything was going fine until she started disrespecting me in ways I don't want to talk about, but it made me worry about infidelity. We tried patching things up but I still saw weird signs. She said she would never do something like that and that there wasn't another guy. Considering her parents had divorced due to adultery it made me believe she meant what she said. Regardless I couldn't forget her many repeated cruel actions and her lack to change so I decided to call it off, but in the conversation she just said she felt that a relationship was too much at the moment because from the way saying things, she didn't feel good enough and relationship was too much for her at this point of her life but at the same it seemed as if me leaving didn't matter to her. A week later she sent me a text apologizing for everything and for hurting me, saying she would understand if I didn't want to respond but she'd always be there. I never even read her message, just left it on delivered. A month later she deleted the message, for me not knowing what it meant.

Another few weeks passed by and I bumped into her in public with another guy and I could tell it wasn't platonic. I don't know what to make of this how did she go from wanting to go slow to having a new bf in two months after a break up?