I'm currently in the process of upgrading my skills - it's like a hobby - and have completed a lot of years of third level study. (A LOT of years..!). I can tell you from experience that exam time is no time to have people ask you for anything, very least of all your time. Your partner should understand that - the pressure is bloody immense. Have him get someone else do it, or get a cab from the garage. You need your family's support.
Oh, and in no way are you beintg selfish.