Transference or not, what you are feeling is grief and loss of a relationship. I would treat it the same as a break up with a significant other or the death of a loved one.

Allow yourself time to feel the emotions and heal from the pain. Also try to remember and focus on the positive and good you received from the relationship.

If it is truly transference and you are projecting feelings from someone in your past onto your T, you may want to consider seeing a new T to work through your issues from the past.

In DBT we use a skill called Radical Acceptance. This would be a case where Radical Acceptance is needed to accept the fact that the relationship is over. At the same time it is important to work on self soothing skills.

I wish you the best.