OH Melissa, I am so sorry. He obviously belonged to someone for him to have collars on him. Please don't blame yourself over this, you can't take in every cat you see on the street, especially if they belong to somebody. It sounds like he could have belonged to Oreo's owner. Is there a way you can find out?
This is one of the reason's I keep mine safe in the house, especially since our street is a very busy one.

That is such a beautiful poem that you wrote.

Rest in Peace little one.

((((((HUGS)))))) Melissa.