I'm upset with my girlfriend over her comments during sex
What did she say during sex?
She said I'm not satisfying her.
Relationships are hard and being honest can be even more difficult. It may have taken her a lot of courage to tell you that she wasn't feeling fulfilled. Talk over the troubles, even if it makes you uncomfortable.
I am going to make her even more unhappy than I did before.
I don't think you should intentionally sabotage your sex life. You just really need to talk to her and tell her how she hurt your feelings.