Hi Christine,
I’m glad to hear you were one step ahead of me and had already attempted to reach out and apologize directly to her. I’m guessing then that you have also tried apologizing to him as well? I agree that the door is probably not closed on this relationship and that if he were already involved with this other woman he probably would have wanted all of your belonging out of his house.
So, if you consider your therapist’s advice to “fight for your relationship”, what does that mean to you? How have the two of you worked through conflict in the past? What have you learned about him, yourself, and this relationship that you can use in this situation? How can you put that information into action to help remedy the split?
It may be time to suggest to him that the two of you start dating. Take a step back from where you had been before all this and then proceed slowly. Give him some of the space and time he says he needs to find himself but still maintain the connection. During this “dating” period, the two of you can address any concerns about the relationship and repair any damage done during this recent incident.