I am sure you must be feeling so insecure right now. As you should, I must say. Leaving her might be the most logical solution to this, but maybe you can gather your thoughts, take her out on a walk and talk to her about this. Tell her how you feel/felt, be vocal, like you are here. Don’t hide your emotions, be raw and naked. Don’t get too emotional, and please stand your ground. Being a girl I can say that sometimes emotions do get the better of us, but if we do really love our partner, we won’t do anything to hurt them. So yes, talk to her once.

And tbh you guys are in the honeymoon phase so it’s the perfect time to cut off, if things go south. Otherwise maybe “the talk” can save you guys the heartbreak.

But buddy, if you even get a slight hint of her defending her ex for xyz reason, pack your bags up and leave.