Flat rear tire on my way home

There's one more free overnight parking slot for the month in our building parking. And, I decided to use it last night.

I left my car at the parking and went home biking using my KHS Alite 150. However, along C5 at the corner of Mercury Avenue in Libis, I was having a hard time pedaling. So, I stopped and saw that my rear tire was flat.

After removing the tube, I checked the tire (Kenda Nevegal) several times but found nothing that caused the flat. So, I replaced the tube with one of my two spares. In less than 5 minutes, I was done.

At home, I checked the tube and found a hole at the seam on the inner side. I'm now thinking of retiring this tube considering that it has four patches already. Or, perhaps, I patch the new hole and make it a spare.