Points are awarded based on your MMR (Match Making Rating). If you win lots of games your MMR goes up. If you lose lots of games, it goes down. If your MMR is that of a different league, you will receive MMR to help you get to that league. For example, if you are in Gold 5, but your MMR is that of a Gold 1 player, then you will get matched with Gold 1 players and receive more LP for a win than a loss. However, if you are Gold 1 and your MMR is of a Gold 5 player, then you will get matched with gold 5s and lose more LP for a loss than a win.
If you had a lower MMR when you started duoing then his MMR will be higher than yours. LP awarding is also loosely based on K/D/A, and objectives taken etc. For example if you feed the whole game but you win you will get less than if you carried your team. Vice versa, if you feed loads and you lose, you will lose more than if you lose but you did very well.