I agree with Anne.
It is dangerous to make assumptions as to how the dog was treated...whether they looked after him or not etc. Sure some things sound a bit odd, but the owner might just be one of those aloof type of people.
If you can't afford vet bills...vaccinations...desexing etc, then you shouldn't have a dog. What about all those unexpected expenses...like emergency surgery etc.
Look...I think it is great you have been looking after this little guy, but I don't agree with the way it has been done. You should have followed the right/lawful avenues regarding handing him in to the pound. The pounds have a bigger chance of finding his rightful owner than you do!
I can understand you state your are attached to this little guy. Rescuers deal with this on a daily basis, but still in the end do what is best for the dog.
Sorry...I can't sit here and give you a pat on the back saying..."you are doing the right thing", when I think you have done things the arse about way. I also agree with Anne that you took him away from the area he was found in, so it is up to you to take him back there for "the owners" to view him.
People here mention what this guy is up for in fines. But by you taking this dog away from his area...not handing he in to the pound IN THAT AREA...you could just as well have stolen him IMO. This guy might have broken the law, but so have you!
Question...if you hadn't found him...would you have considered getting a dog anytime soon? How do you know that being with you is better for him than being with either his rightful owner or someone coming to the pound who REALLY wanted a dog and could afford it?