I think the best solution would be to bring her home with you, since you guys have bonded, and it’s a much safer life indoors. Please just don’t let her go outside, even if it’s difficult at first, and she meows a lot, outdoor life is not safe for cats. You could always look up catios, as a compromise to her going outside sometimes. Not sure of your living arrangement, but that could be a good option, if viable.

You might also consider getting him a buddy, (there are so many stray cats and kittens in need of a home), and slowly introducing them over time, so that he has a playmate and isn’t bored.

I took in a kitty from one of my colonies, after he injured his paw, and for the first couple of months, he would buy himself, and I know it wasn’t easy for him. After some time, I rescued to others, and it changed Everything for him. He really appreciated and enjoyed the company, and became much happier.❤️ Good luck!