You are certainly not a bad parent, and definitely not alone! I can't stand leaving my 5-month old Joonie alone even if I just have to run to the store, let alone my day job :( I hate the thought of her being sad at home, wondering why I left and asking herself when, or even if, I'll be back. I always feel incredibly guilty!
But it's all so worth it when I walk in the door after a long day, and I see her sitting there waiting for me right on schedule. I get the best greetings and purrs from her after not being home for so long.
I don't think you need therapy... And if so, then you're definitely not alone! because then I need it too :-P