How can I make amends with the one I wronged? I had been cruel to a cat before and it bothers me a lot that I had been unkind to him. He's been dead for more than a year but I still think about how he suffered because of my callousness at the time. Is there a way for me to send him love now, or any way I can make it up to him somehow?
The Kamma has been laid down.

Now there's no use in scruples over the past.

The best and the most constructive thing to do I think is make a commitment to never repeat acts of callousness and actually fulfil it.

It is possible to mitigate acquired new bad Kamma, counterbalance it as it were, by development of wholesome qualities such as good will, cheerfulness and compassion.