What would you do?

I have two male dogs who have lived together for 13 weeks with no problems. The other day the puppy(14 weeks old) was sniffing around for food the big one had spilled(big one is 2.5 years). Big one is protective of food and so he snapped at the little one. I went inside after I was sure all the food was gone. As I was about to leave to take my friend home I heard the little one SCREAMING. The big one had bit him(looks like it was just one bite and he let up immediately) the little one is fine now and his wounds are healing with my help keeping them clean. Today I put them together again and the big one was just excited and happy the little one was back. I’m afraid to leave them loose when I’m not home or awake to watch them(outside only dogs). What would you do? I’m afraid something will happen and I’ll lose them both. But I don’t want to separate them because the little one has only ever known having the big one there. This is one of the toughest decisions I’ve ever had to make