You need to get in touch with the Fish and Wildlife Department for your state (if there isn't a local office you'll need to go to the state capital). The laws for wildlife differ from state to state. I don't know much about opossums - not sure if they carry rabies, etc. In some states it is totally illegal to keep any sort of wildlife as a pet, in some states you can actually buy a wild animal to keep as a pet.
I am not trashing you, but I hope you think of what is the appropriate thing for the animal. A "wild" animal deserves to live his life as he is supposed to - with others of his kind. You say you don't think he could fend for himself at this point but that may not be the case. I urge you to find a local wildlife rehabilator who has experience with opossums, preferably someone who has one or more. He/she would quickly learn how to act like a wild animal with the influence of others. If you can't find a rehabber I would suggest that you see if you could place him in a nature center.
When this little guy hits sexual maturity your sweet little baby is going to change completely. Those guys have vicious teeth and know how to use them. And regardless of how he acts now he isn't going to be your friend then.
I'M NOT TRASHING YOU!!!! I was a rehabber for several years and know what I'm talking about. I KNOW the attachment that can be formed; I've cried several times when I released animals. I know the feeling of having loved and cared for a wild animal then have to have it put to sleep because it bit me and it had to be checked for rabies. I've watched animals pace back and forth in their cages because their internal clocks were telling them that it was time to have a mate. Sometimes you have to love them enough to let them go.
Please let me know what happens. I never loved an
opossum but I've loved other animals and I care what happens to both of you.