My Twin Sister's Mate Is Now Mine

I was the biggest curse to my pack and an even bigger one for my parents. They made me my sister's Keeper, and I did everything I could to keep her safe, but it was never enough for them.
I found solance in the love I held for the alpha of our pack. I loved him even though I knew he didn't feel the same way. I thought I could still win his love, but my heart was shattered when I found out he chose my sister as his mate. I couldn't take it anymore in the face of his rejection. I packed up in the middle of the night with no plan and nowhere to go, but I found myself a new home.
5 years later, l got a call that my sister had passed away. A part of me didn't want to go back, but if I didn't, then it was a decision that I was probably going to regret my whole life.
I came face-to-face with the man who rejected me, but that wasn't the only highlight. I was surprised to see a sweet little boy who wouldn't let go of my leg and called me mother. I had to marry Arnold in order for him to grow up happy. But where do I put myself when my twin sister returns?