Kiki
Our cocker is now 8 months and follows me A LOT more than my partner, but that's because I'm more doggie focussed and do much more (and sometimes all more!) of the feeding, walking, playing, training and grooming.
Dogs will focus on one human at the expense of others, its kinda understandable that they bond more with the one that gives them the most or responds the most.
Initially our cocker would bark when I left the house but not when my partner did.
I then started a programme of leaving, without fuss and walking round the block, so just out the house for 5 mins, I did that three times a day and within a week notices less barking on me leaving.
Inside the house, I'm doing the 'close the door and leave for 1 second, 90 seconds, 10 seconds, 3 mins, 5 seconds and so on to keep the dog off balance and no clue how long I'll be gone for. I return when I decide, not when he barks or scratches, but always within 3 mins.
Over time I'll build that up. My record - or to be specific the dog's record - is 15 mins with no barking, scratching or whining.