Was used and dropped by a girl. She has a bf, should I tell him?

I was approached by a girl online and over the course of 2 months we developed a romance. We were so close, and made concrete plans to fly and visit one and other. Part way through she explained to me that she had a partner, but that he was more or less just a friend and the she was only with him really for a place to live and because he supported her, that he was her best friend but she wasn't attracted to him and it was only a matter of time before she left.

She moved home to her parents to continue developing a connection with me and it was so lovely, we fell in love. But her parents wouldn't let her stay permanently and she had to move back with him, staying in the spare room. Then all of a sudden she went quiet. She barely spoke to me for a week and then explained that she is giving it another go with her partner but would love to be my friend as she genuinely cares about me. I was upset but I do value her a lot and want the best for her so agreed. However, she has been ghosting me ever since, I haven't spoke to her in 2 weeks, despite trying to initiate conversation only to be ignored or sent a short and closed response. I sent her a heartfelt and sincere goodbye message a couple of days ago, because I deserve better than to be dropped and ghosted, and she still hasn't even read it.

Now I just feel angry. I feel like she used me and that everything she told me wasn't true. How can you care deeply and have strong feelings for somebody, and yet just drop them and ghost them suddenly? It seems all too easy for her. It makes me wonder whether this is the first time she's done this with a guy behind his back, I doubt it. It's also clear that she's only with him because it gives her an easy life. I bet she'll find another guy to get into soon.

I'm now strongly considering the option of sending him screenshots which show how we were, what she thinks of him, nudes she sent me, proof of flight tickets etc. She can't get away with screwing us both over and then just happily forget about it until the next time, this needs to end and I'd want to know if I were him. What shall I do?