How much time i have to wait before Dermin decide to show him, i have already wait two tweeks from Galvarey's death even if i am in romance with Jaheira?

I think that Dermin is part of the Jaheira romance. Sorry I can't rememebr if he is part of the overall harper quest and so romance independant. If he is romance dependant then you must be aware that much of the time dependant events in romance run in real time (i.e. how long the computer has been switched on). So resting and traveling to waste time in the game world makes no difference. In fact it can actually cause problems as key events get out of sync.

Anyway if you want some other views on what might have gone wrong or how long you should wait try here:
http://www.sorcerers.net/ubb/Forum2/HTML/001746.html

You could also look at the romance guide from Sorcerers as I think it explains what value certain variables need to be before Dermin will appear (the love talk rating):
http://www.sorcerers.net/Games/BG2/index_tips.htm

Use the search/find option once you've downloaded the romance guide to look for Dermin.