She sounds like someone with some control issues. Getting mad and throwing a tantrum till you comfort her, shutting you down when she doesn't feel like talking about whatever topic, etc.
Personally it's someone I wouldn't get along with on a friend level, let alone a significant other.
This doesn't seem to be about the animals. Like you said, number of snakes hasn't changed, you're getting a different one in place of a snake you rehomed
Don't really have any advice as I'm the world's biggest pushover, but this really doesn't sound like a healthy relationship. I hope you can work things out to where you're able to make yourself happy though.