Who is this Perfect Girlfriend I keep comparing myself to?

What is it about this hypothetical woman that makes me feel so bad about myself? I don't know where she comes from, but I can see her so clearly

It was as I wobbled poorly through a yoga session first thing this morning that I thought of her. Perfect Girlfriend, a strange ideal I have in my head whenever I'm feeling particularly flawed, low energy or grumpy. She’s my parallel universe rival and I am fully aware that she does not exist. Yet she bothers me.