It doesn't matter. Kivan's code checks for Kelsey, even without the CBP. As soon as Kelsey joins, your influence with Kivan drops by three points. You get them back when you dump Kelsey, but don't go to Spellhold at that point, or Avril will say that Deheriana is in Arvandor waiting for Kivan. If you become committed to Kelsey a any point, your influence with Kivan drops by 10, but you only get 5 back when you dump Kelsey. So yeah, if you're planning on romancing Kivan, you'd be better off breaking it off with Kelsey as early as possible.
But yeah, it's a real shame that the older NPC romances don't give you a chance to let the guy down gently.