You loved him. You were not ready to let him go, so you tried everything. I did too when my dog Nala was found to have a heart-problem that turned out to be cancer. I took her to a specialist and I got an extra month with her because they emptied the fluids out of her heart. I don’t know if it was the right thing to do, you can never know these things. I just couldn’t let her go without trying everything, she was like a part of me. I keep her ashes in a book-shelf.
It’s been 7 years now and I think of her often, but now it’s mostly happy thoughts, because she was a happy, goofy, wild little girl and I’m so grateful that I got I got to have her in my life. She too helped me through a lot just like Bright helped you.
You did everything you could for Bright, you made his life so, so much better, he was so lucky to get you for an owner. And you were lucky to get him for a pet. The downside to love is loss, but it is always worth it anyway.