Am I mentally ill or it is normal (imaginary gf)

I have created a whole person in my mind that doesn't even exists in real life. Her eyes, her face and emotional behaviour. Honestly nothing is better than that. I talk to her I imagine her. I have created her for like past 1year and we are best friends. I don't know it is normal or I should get a checkup. It could be becouse of my lonely childhood and present circumstances.