I really think he is just terribly excited when you come home and is leaking a little bit. The urine sample can be checked to see if he might have a little infection, too. Mention it to the vet. Also, if he ever begins to have problems someday, there is medication to help that, too.
I understand your fear of losing him. I did the same thing at times with Muffin. But I really want to urge you to enjoy him and not get so upset before the vet ever gives you a diagnosis. Also, he can sense your emotional upset and it upsets him, too, because he doesn't know what is wrong. Enjoy him now and worry later!