Just try to work through your feelings rationally.
And have a cup of tea and a biscuit, at least.
You feel anxious, and then you feel guilty that you feel anxious.
You’re anxious about the responsibility, that you need to be responsible.
You worry that you’re not enough alone for the dog, that you alone aren’t capable of putting the dog’s needs first.
But you are. These feelings are temporary.
Try to break down what the fears are, then challenge your fears. Have you ever had CBT? If so are you familiar with how to stop catastrophic thinking?
Do you fear you won’t be able to go out alone? An example of catastrophic thinking would be
The dog is sad when I go upstairs and whines. I’ll never be able to go out alone and be trapped with the dog always. I’ll never be able to meet friends at the pub or go window shopping or [insert your preference here]. My life is changed for ever. I can’t have a dog by myself because can’t cope with being trapped and I can’t make the dog sad.
But you can challenge this thinking.
You said you’d gone out for 30 minutes, with no issues , and the dog slept alone last night. Greyhounds aren’t particularly prone to separation anxiety and like to sleep for large parts of the day. Once your dog is settled and feels more secure with you he’ll almost certainly be OK and you can adapt your schedule around him. If you want a longer day out you’ll get a dogsitter - perhaps you can research some options now - etc.
Like I say, you can give him back and that’s OK. No judgment. But you felt sure you wanted this and that means you probably - underneath the panic and anxious feelings - can do this and be happy, if you can challenge your anxiety and tough this period out.
What’s your favourite easy meal? Mine would be pasta, butter & cheese…