Both reactions/responses would be "no bueno". Be cool to her and simply be cordial at all times. This is the most you owe anyone. Technically she hasn't done anything wrong and has the right to talk to anyone she wants. Unless you're married to her or she has had children by you, she owes you nada.
The more spiteful you act, the more reason she has substantiating why she should never have spoke to you. Also remember, whoever she's with, there's very little chance this will be her future husband...so you're not 100% out of her view. If she's paying ANY attention to you at all you have SOME value (not sure what category that would be...only you would know).
All is fair in love in war, especially if there's no formal commitment. Get on with your life, do not attempt to punish her. Getting on with your life will be "punishment" enough and on top of it may spark more interest.
Last year I was talking to a girl via FB I met on POF. I was overseas so I could not act on her face-to-face. In the meantime she was going out on dates with other guys. I went NC with no announcement. She would check on me every 8 weeks or so I kept things "cool". Fast forward to last week, we met in person and she gave "it" up to me (invited me back to her place). Even now, our communication is sparse, but she hasn't stonewalled me so I'm just staying cool and dating other women.
Be the cool rich dude from Meet the Parents. Don't "squeak" about non-communication and congratulate her if she announces a new relationship. Eventually all women want to know what you've been up to (at least in my life). Don't always make it about sex...because everyone gets that right?? If you go in with the attitude that everyone has (fill in the blank), then it comes off as a non-preassure situation and she'll more than likely respond to that in a far more positive manner.
Dude, I've been rejected I can't tell you how many times. I've been cheated on a few as well...maybe more. I've also had a ridiculous number of successes and I've had HB5-10. I don't always know what the secret formula is, but I will say that the above advice has brought me many carefree years with minimal anguish.
Give it a go. Good luck.