hello there, i have adoted a chihuahua from the shelter about a year ago and when i first brought her home she was the meanest thing ever, soon as i put her down she fled for under the bed and she stayed there for a few days i thought how was this gonna work out, i thought she would never come out, but a few days later after seeing me leave her treats and food and water, she one day had a complete turn around and totally became my friend and now she hates when i have to leave too but she doesn't have the separation anxiety that your having so i really can't help you there, it will just take some time to get over it but i am sure with a little work she won't have that anymore Chihuahua's are wonderful dogs and they will always be by your side no matter what