Hey Mic and welcome
A good week followed by hurtful behavior towards you, and then (it sounds like) repeated over and over, would be a lot to cope with. You must really be wanting things to change, especially because it's your fiance, and so you'd like to build a life together, not be stuck in conflict.
How long have the two of you been together?
Have you talked about your feelings with her? If so, how did that go?
Am I tracking with you that infidelity, or even "just" the appearance of infidelity / emotional affairs, is a dealbreaker for you? Does she know that?
This is painful stuff to be in, and while there are no easy answers, talking about it here can help you get clarity on what you want in your life and what paths forward might be open to you, that you haven't considered yet.
Fill us in some more, whenever works for you;
kells76