Then break up with her NOW, if she was a good one - this way you will remember her being good.

I "overslept" with both ex H's. Should have broken up earlier for the sake of good memories. As it becomes less intense, sex-life-wise, it gets worse and becomes mechanical, which is very boring and not worth your time. It is better for your sake to break up while it is still intense and has not become mechanical (it is ALREADY becoming mechanical since you report her not reacting to the kind of suckling she used to react to), because you will then retain good memories for life. A few more sex acts now, of worsening quality, are not worth remembering it at its worst and not at its best.

This is not something you can realize by yourself because she is your first one so you do not have experience.