I am sorry for all that you are struggling with. Given the time and effort that you spent with the dog, I can imagine that you formed an emotional bond and are grieving the loss of it, too.
I certainly understand the feeling that she got away "scott free." That sentiment comes up on the boards often. However, I noticed that you said that:
She's been trying for the past year to get me to take her back; she's been saying the balls in my court; and the "accidental" picture thing.
This all suggests to me that the relationship with the "super successful" guy isn't so super.
It also sounds like you are somewhat down on yourself for grieving the loss of this relationship, but it sounds like you have good reasons to be grieving to me.