Help with identification

[Charlene89]

Hi I am not sure what type of garter this is but it mostly resembles an Eastern or black necked in my own eyes but I thought I could get some input. It's not exactly a pet of mine. In October we had 2 days of 80 plus degrees outside and I was coming up my driveway and seen it. I brought it in to share with my son. Well the next day it was less then 50 outside and I didn't know they brumate and the local wildlife people told me it would freeze if I let it go. I kept it and it wouldn't eat for nearly 3 weeks no matter what I offered(works, crickets, minnows). But I finally found some guppies (live) and it ate like a champ! I read that live dish are bad for them cause parasites, but it is wild. Still I didn't want it to get sick. So I decided to put a thawed pinkie in it's water and it ate it so now it eats pinkies. I feel so bad, but I'm keeping contact down to a minimum to see if I can release it in the spring but I'm not too sure because its so calm. It's never struck at me. I've held it to remove it from it's tank to clean up but that's all. I'm so unsure and I don't even know what kind of garter it is.