I understand you are having kind of a hard time with Ethan. Pretty much, as you see it, he's a devil baby that has come into your life as some sort of punishment for some unknown crime. He's stolen me, your mother: my lap space, my time, my energy, and my love. I feel unexpectedly guilty about this. You are so small and so cute and it breaks my heart for you to feel thusly abandoned.
However, as I thought on this, I realized that I was you once. My mom had a baby 18 months after she had me. I was that older baby: abandoned by her mother for someone smaller and more helpless than myself. And, you know what? In my conscious memory, I cannot think of a time when I felt it. I don't remember thinking that my younger brother was a devil baby. I don't remember ever feeling like I didn't have access to my mother's love or time.
This gives me hope that this phase will be short-lived, or at least, that you won't remember it.