Among all addictions - betrayal is, perhaps, the most potent.
The sad truth is that those who have betrayed you once will most likely do it again.
When that filth is within them - it rarely washes out. It is the ultimate cry for help, and an act against one's own soul.
Self-sabotage, subterfuge, survival-mode thinking - these are all traits carried by these types, and no matter how much safety and containment you provide - they will always find a way to twist themselves back into dysfunction.
Unless they truly, truly repent - and change.