Hi there,
Welcome. I'd respectfully disagree with your therapist that it will take you "a lifetime" to heal. I wouldn't tell you to "let go of it and move on," either, because it IS a process and it DOES take time and work, but you don't have to nurse this hurt for the rest of your life.
Many of us here have lost loved ones to this disease, and it really is tragic. But it's nothing we can control or cure or magically make go away.
Have you been to Al-Anon? In my experience, and that of many others here, Al-Anon was the lifeline that saw us through the worst of the storm and helped us to come out healthy and whole on the other side. There's something about being around people who really GET how you are feeling and what you've been through, and Al-Anon has tools to help you refocus on your own life so you can move ahead.
If you choose to wallow in sadness instead, then you are doing the same thing the alcoholic does when she rejects help and insists on going her own way. Right now, it isn't just what she did that is hurting you, it's your reaction to it. The pain of the loss is inevitable in these situations, but prolonged, lifetime suffering from it is not. That part is optional. But there is work to be done if you want to climb out of your misery.
Hugs,