You're not horrible, Maria. Don't be silly.
The apartment I lived in prior to the current one, is located right beside a busy road. I had two cats while I was living there and they both wanted to get outside every now and then. I did let them out when I was at home, but one day I saw Chewie cross the street while a car was approaching and it was a really close call - an inch further and Chewie would've been hit. I decided there and then that they couldn't go out anymore, but I always felt bad about that decision, because I knew how much Chewie loved it outside. Fortunately, he's a very easygoing cat and he was alright with it until we moved to this apartment, where he can go outside again.
30 years ago, my parents made the same decision for their cat as I made with Chewie and for the same reasons and it didn't work out too well; their cat tore the whole place apart and managed to escape anyway, so he could tear the neighbors' places as well. They finally had to put him down.

Making decisions about quantity and quality of life always is a hard one and I myself am always wondering if I made the right decision. Sometimes it turns out it was the right decision, sometimes it doesn't. So don't be so hard on yourself - you did what you thought was best.

I do hope Felix will show up again. There's still hope.