Hey guys, currently redpill in training so bear with me. Hoping for someone to chime in and let me know if I'm handling this in the correct way.

A bit of background, I've known this girl for about 3 or 4 years, we've been hooking up on and off for most of that time. She had a bf for about a year and a half and cheated on him with me. I then fwb'd her since they broke up and have admittedly spent too much time with her and have probably put in more investment then I should have. Nothing too serious but more than a fwb should receive and enough that this current situation has pissed me off and affected my frame.

A few weeks ago I went on holidays for a couple of weeks. During this time she was invited by the people she babysits for to come with them on a one week holiday. They have a cousin that they have been trying to set her up with and he was going with them on the same holiday. Obviously you can see whats coming from a mile away. While I was away I had a pretty good idea that she was hooking up with this guy and she was being distant so I soft nexted her and didn't contact unless she contacted me. About two days before I got back she started full on messaging, calling, etc. again. I put the holiday thing to the back of my mind, chilled with her once and she's fully back in, not distant at all, seems like nothing happened, saying I love you (I didn't say it back), how we have such good sex, etc. Probably realized the other guy was beta or whatever.

Yesterday I ran into a friend who essentially said they did hook up for those two weeks. This pissed me off even though I already knew it. The fact that I handled it in this way and that its pissing me off is telling me I should hard next now. She has no idea that I know. So we were supposed to hang out today but what I've done is basically said "I'm busy something came up", she's currently freaking out sending me a million messages (which further reinforces to me that she knows she's done something wrong). I figure I shouldn't bother telling her anything even though I really want to and just go silent now. Admittedly I'd really like to keep her around as a fwb but from my own reaction to the situation I think this is the best course of action as I'm probably too invested or else I wouldn't care what she was doing when I was away. I want to make sure I'm handling this is the right way, any advice? Should I keep the fact that I know to myself?

Edit: Thanks to all the responses, appreciate it