A New Sibling!
While some humans can be terrible, terrible people, others have hearts of gold. For instance, the OP took time out of their busy schedule to look for a permanent home for this stray black-and-white kitten. However, what they didn’t realize was that their pet cat had an even bigger heart than them.
Instead of finding someone to adopt the stray, the OP’s cat decided to take its little buddy in. How will it provide for its tiny buddy? It won’t—it’s your job to live with whatever life-altering decisions your cat makes on your behalf. Good luck with your new kitten, OP.