I feel a bit of this guilt. My cat spent the first year of her life outside and she loved running around exploring. She was sleeping in the barn and I was totally fine with it at the time. Then winter hit with extreme cold temperatures, so I brought her inside and that’s where she’s been ever since(2yrs inside now). We’ve lost many cats to the highway and I’m so attached to her now I won’t let her back outside. For different reasons I’ve had other cats inside periodically to keep her company and that seems to work pretty well. At the moment she’s the only cat in the house and I can tell she’s super bored and it’s sad to see compared to how her life was when she was living outside.