Dear Josh:

You wrote: “I have such a hard time comprehending  how something that hurts so much emotionally, physically, and mentally  in my end can feel so liberating and necessary on her end.”-

reads to me that she has been unhappy in the relationship for a while before she finally exited it. That must have felt liberating to her, to exit a distressing situation. Because you were not aware of her distress while in the relationship, it is when she exited the relationship that your distress started.

Then she got involved with another man, her attachment need satisfied, at least partially and temporarily, for now. On the other hand, you did not get involved with another woman, and so, your attachment need is unsatisfied.

Sometime in the future, the situation will change- as the two of you, likely independently of each other, get attached and unattached, re-attached and so forth.

anita