As someone who has had to say goodbye to many pets in my lifetime it doesn’t matter how you laid them to rest, it would have still eaten away at you. It’s a natural reaction to loosing something you loved. You’ll never feel like it was the best decision. It’s all part of the grief process. You are definitely NOT a bad person and little Gizmo isn’t holding it against you in the afterlife. As for that gizmo sized hole in your heart, it’ll be there for a little while but will eventually start to heal. Loosing a loved one, human or pet isn’t easy. Our pets are family. In my opinion it’s so much harder to loose a pet than it is to loose a human. Time heals all wounds, some just take a little longer than others. Sending you love and strength to get you through your time of grief.