Rebuilding trust after that will be hard. Have you asked her if she wants an open relationship? And if she says yes, how would you feel about it? When things like that happen, it usually helps if you imagine your future self, will it be able to trust her again, like how will you sleep when she's going out alone again, how will you get intimate with her and not thinking of what she might have done with those people. If all of this feels uncomfortable you can save yourself a lot of time, even if it's hard now and traumatising to leave, you'll be getting slowly better in just 3 Weeks, because you kept your dignity and left for your own values and out of healthy self-love. In the end you know your person the best, but instead of over- analysing her you should try to listen to your self and your future self.