Its a pet name. He obviously thinks about you then:) As either a good friend or possibly likes you as something more.
Its a good thing, like a pet name he has for you, its affectionate I think and cute, its a lot better than bitch, so I would not worry!
It means, "My baby" or "My Girl, or my homegirl. Its just a cute name people use with someone they like or with. Its boo boo or boo