It's because you love her. And there is absolutely no shame, or weakness, in that.
The rollercoaster, as often described on this site, reflects the up and down, back and forth feelings that accompany the recently betrayed. If it makes you feel any better, 2+ years out I still sometimes get pangs of absolute contempt despite a remarkably successful reconciliation.
It is up to your wife to get you off the rollercoaster. I hope that she is up to the task.