Hi, I'd like to help you with your question.
Yes, abusers can learn to stop abusing and controlling. The first step in the process is to realize they have a problem. Insight into what they are doing and why they do it takes a bit longer, and usually goes better if the abuser sees a therapist, like you mentioned in your post.
However, even with therapy, the abuser must follow the suggestions made in therapy and also do their own work outside of therapy to keep themselves progressing. The use of books, support groups and other means of educating themselves helps the abuser to learn how the behavior started, how it manifests itself and how they can use techniques and insight to stop the behavior.
Here is a book that can help you:
The Verbally Abusive Man, Can He Change?: A Woman's Guide to Deciding Whether to Stay or Go by XXXXX XXXXX- although this book addresses verbal abuse, it has the basic techniques needed to understand how the abuser can stop their dysfunctional behavior.
It is good that both of you are in therapy. Sometimes, people feel it should be only the abuser or person being abused that goes into therapy for help. But the affect of abuse can be deep and damaging. With both of you seeking help, it will speed along the process of healing.
Hopefully, with help, the abuser in your life will recover and you will as well.
I hope this has helped you,