Feeling off after adopting a second cat—wasn’t expecting this emotional rollercoaster

I adopted a second cat about three weeks ago to keep my older kitty company, thinking it would be great for both of us. The new cat is sweet and playful, but since bringing her home, I’ve felt this weird mix of guilt and anxiety. My older cat seems stressed and hides a lot, which makes me feel responsible and sad. I’ve tried keeping their spaces separate, giving extra attention to my older cat, and using calming sprays, but the tension hasn’t eased. On top of that, I find myself more irritable and restless at night, which is unusual for me. I was hoping this would be a happy adjustment period, but instead it’s been emotionally draining. I’m worried I made the wrong call, but I also don’t want to give up on my new cat. Has anyone else felt unexpectedly stressed or guilty after bringing a new pet home? How did you manage those feelings and help your older pet adjust without it taking such a toll on your own mood?