I'm sorry to hear that - it's never easy, but over time it should get easier. You will never forget him, but hopefully will look with fondness rather than sadness.
I'm so sorry about Buddy. It seems natural to me that you still miss him a year later. I miss cats and dogs that passed away years ago. They get into our hearts and once there, they stay. In that sense, they are always with us. I hope with time you will find comfort in happy memories, though they be bittersweet.
Guilt is always present when we mourn, there are always all those should haves, could haves. You didn't do anything on purpose, so anything done unintentionally is an accident, you had no idea and no control over what happened. Buddy would not blame you for anything, he loved you and would never want you to feel so sad. Of course you miss him, he was a part of your life, and your heart. Even though he is no longer in your life, he will always be in your heart, nothing can take that away. Try not to make yourself miserable by thinking of the worse, he would never want that for you, try to celebrate the love you two shared instead, and pass on that legacy of love he left you. I haven't found that 'special' one yet, but that doesn't mean I can't love and care for the countless others who so desperately need me. I do this in my Chrissy's name, and I know she would approve. You have proven you have a big enough heart to share love, and yes it hurts so bad when we lose those that we love, but it is still better to have known that special little 'Buddy' then to have never known him at all. We all here at this site mourn with you, know you are not alone. I'll keep you both in my prayers.
Be gentle on yourself and take care...........dear sweet Buddy, try to give the one who loves you so much some kind of sign that you are at peace, wherever you are........
Honestly at the old place we lived we had our closet door open and suddenly like a cat ran in there you heard a big crash in it and we even was looking directly at it and Tabby never walked out and you couldnt see her in there so me and my husband who seenbit too said it is buddy