I’m guessing this story is more than a little bit embellished,
Your proof that she was “ripped by him” is that he was lifting her up and kissing her? That could’ve been something consensual, or that could just as well have been a sexual assault you were witnessing. Also, her kissing him doesn’t mean she had sex with him, and so fucking what if she did? As long as everything was consensual, who cares? Well, you, apparently, but it sounds like she’s smart enough not to date you.
And of course you think it was all about you. Why on earth would she be thinking about you and a bunch of other guys during a kiss?
That is how fucking self-centered and entitled these assholes are. Typical incel: “Oh my god, this girl I hate but want to have sex with is kissing some other guy! She must be thinking about me and how ugly I am.”