I can't take this pain anymore.affair/separation/divorce?

[Problem Girl]

We were married for 15 years when my husband started having an affair. We have 3 kids & had just built our dream home. I tried for 2 years to stand by him & get them to stop. I even talked to her. I asked her to have some respect for me, my family & kids & leave my husband alone. She responded, I'm sorry you are being hurt but no, I won't. My husband & I were best friends. I asked him to leave her alone, he refused. I asked him to leave the house, he refused. So, I was forced to leave. We have now been separated for a year. I have lost everything, my husband, best friend, daily routine, lifestyle, being a mom everyday. He lost nothing. This pain is killing me. To see him going out of his way to spend time w/her when I begged him for years to do things w/me. I am constantly playing in my mind"why wasn't I worth it", "how could he have done this to us" I feel worthless. I am in so much pain.The thought of her becoming part of my kids lives makes me sick. How do I stop feeling so bad?