Nothing you’ve done has “made” your baby develop separation anxiety. It’s a perfectly normal and important developmental adaptation.
Nearly all children experience separation anxiety between the ages of seven and 18 months. Some have more intense reactions than others, and for some, the stage lasts longer than others, but almost all babies have it to some degree.
The development of separation anxiety demonstrates that your baby has formed a healthy, loving attachment to you. It is a beautiful sign that your baby associates pleasure, comfort, and security with your presence. It also indicates that your baby is developing intellectually (in other words, she’s smart!) She has learned that she can have an effect on her world when she makes her needs known, and she doesn’t have to passively accept a situation that makes her uncomfortable. She doesn’t know enough about the world yet to understand that when you leave her you’ll always come back.
She also realizes that she is safest, happiest, and best cared for by you, so her reluctance to part makes perfect sense especially when viewed from a survival standpoint. Put another way: You are her source of nourishment, both physical and emotional; therefore, her attachment to you is her means of survival, and when she reaches a certain level of intellectual maturity, she realizes this.
This stage, like so many others in childhood, will pass. In time, your baby will learn that she can separate from you, that you will return, and that everything will be okay between those two points in time. Much of this learning is based on trust, which, just as for every human being young or old, takes time to build.