League is one of those games that you have to know the enemy champion good if you want to efficiently outplay them, it's not like easier MoBAs that you don't know shit about the enemy character's abilities but still come up on top without a scratch once you know your character. You gotta know your limits and estimate your damage outputs at all levels of the game and consider possible outcomes of each action you make, selecting the one with the most beneficial outcome for you and your team!
Your answered your own query with your first line: "e "Why does he gets a free heal on his ult? WTF? I didn't read his kit, until after I 1v1ed him"
Not knowing how he can turn the outcome of the battle was your mistake, especially knowing his clone is visible to the enemy team meaning he has his ult, whenever it's not visible he doesn't have it, if the clone was invisible to your team he would be broken.
You must accept defeat, learn from your mistakes and be positive and honorable to the better player (who knows you might become friends) and when your learn info about the game you'll climb the ladder and walk the path of TOTAL OWNAGE!!!