aldazir: well, take this for what it's worth, as I'm a newb
I had romance problems too.
I progressed too quickly because I went melee = not enough play or game time/rest
With Jeheira, after the first Harper Quest, it takes some time, but they send "messengers" after you.
This is after you are asked to go to the Harpers Hold and Jeheira takes your side.
First, I think it was a woman(...forgot name); then Dermin(?) comes; then Dermin comes again and threatens death etc...
I was just killing time going from map to map ... finished up my Ranger questing(... I am a Elf/Archer) ... and Jaheira "leaves your party" to go back to the Harper building(...2nd floor)... someone says: "I saw this note here and gives it to you" = I guess she leaves to save the group OR face her accusers ?
Not sure ?
Anyways, I just went there ASAP, and told her: basically, you're with us/ I need you etc....
Something like that
She then leaves the Harpers and is "all yours".
I hope that makes sense/helps ...I know it sounds convoluted = I can't remember the exact progression; I'm just winging it
I sensed there might be some more plot to follow, but I was progressing to the Underdark etc, and didn't want to kill more time.
Anyways, I'm in ToB and she's still with me.
I would suggest the pocketplane "Flirtpack" .... it's mentioned in the "Mod sticky"
Maybe someone with more experience can give you a more detailed Jaheira romance progression answer.