I'm the slower one out of our 'pair', myself and my OH. When we ride together, I pace set and he carries the 'kit' (lunch, spare meds & bike spares etc). Longer rides usually work out that I am the one supporting him by the end - having paced him correctly for him to manage +60/70 mile rides. On hills when I run out of gears (11-28 cassette) I know he already has (12-26 cassette) and will tell him to go on ahead. I used to get frustrated that I was always the slowest, but now I just accept it. I have other strengths and they come in to play at the end of the day when he is worn out. He is the sprinter, I am very much more endurance/distance.
How you train together is difficult - most of my riding is solo, but it could be a better option to sign up with a local club. You can still ride together, but once a week you both would get pushed harder amongst others of the same speed and he would not feel like he is holding you back as much and the club would 'support' him and help him find his strengths as well. (I am assuming here that you would cycle different routes with the club at different speeds etc - something my local club does.)