Hi Gumiisland,
I believe you need to bond with them for the chapter quest, but beyond that it shouldn't matter as long as you don't get romantically involved. Hope this helps
Also I think it's interesting that Jeth and Watermage have some cross over appeal. Maybe because they are both obsessively attentive lol. Jeth sort of sees it and is a bit threatened by it. He picks on/ bullies watermage particularly during the war if you have them battle each other.
Spoiler for ADW
Also tries to pull this same tactic in ADW if you choose to cooperate with the Crown. Choose to work with the crown if you want to see Jeth crash out here and there on bonding convos because he was late to the party lol.