Recently I started playing with a friend, we are 1 rank apart and most of the matches we get even 1 rank higher, why is this, why can't the game search a bit longer to give us a balanced match?

Can someone explain to me how mm works in this game? I was p1, i have 7 lost streak and im g3 now, lowest rank i was playing against was diamond 2, highest rank i was playing WITH was p3. My friends has d3 plays worser than me and she plays...