I'm thinking about breaking up with my girlfriend because she's considering having sex with others for financial benefit.
How does that make you feel?
I feel so angry that she would even consider doing that.
If you do not want her to do that, and she still insists, then you should end the relationship. You both need to be on the same page about finances.
I want to punish her. I want to see her suffer and I want to hurt her.
Wanting her to suffer is going too far. Just end the relationship if you cannot agree on the terms. It is good to prioritize the happiness of both of you.