Seeking advice from high elo players

Okay so I've been in gold for the best part of a year now and I've dipped between high gold and low recently but my question here is how do you guys in higher elo play from behind and make comebacks? This question is mainly due to a game I played last night where I snowballed every lane, I was playing jungle Elise; every lane was ahead, we had all objectives on map and we had 3 open inhibs on the enemy team...yet we couldn't finish, a notable issue I was seeing as due to our Galio and Leona diving when we're not fully grouped and this inevitably threw our lead.

Now, I've just been playing a normal against a Diamond top laner; I took his Riven, I checked his stats after the game finished and I noticed that even when this guy is 13 deaths down, he still wins his games and this is a huge majority of this match history I noticed he was negative almost every game yet he still wins. I can understand stalling the game and waiting for opportune moments to make a play happen but how exactly do you go 3/13 and not lose? If I'm to go 3/13 in any of my games, that game's a straight loss. How do people win from behind?

Yours truly, a Gold Skrub