You are caught in the trap of grief. Grief is normal, when we lose someone we love - whether by death, separation or the person running off with someone else. But a year is about the upper limit to get over this.
I know you said you are going to pull away and I applaud you. But just to remind you again. You were with her only 4 years. Since she ran off with another man, you have been pining for her for 4 years. You don't want to go into missing her and grieving her for 5 or 6 or 10 or the rest of your life.
There are real life grief support groups. You might want to find one, and go listen to the stories and share your own. And definitely do not have any contact with her. Just send her one note, say you do not want to see or talk to her any more. Then stick to it!
You may think she is your soul mate (which I do not believe in, because it is not anywhere in the Bible) but I think she is a manipulator, who decided to have her cake and eat it too! You don't want to be the cause of the breakup of her marriage, do you? Because that is what you are flirting with.
Praying you make this break and for good!