You didn't finish it to fast.. Viconia is just shy about her romance. You've got to give her a lot of time

. My romance with her didn't finish either but, eh.. who cares?
Never played solo through the game but i suppose the thief is the way to do it. Or maybe a wizard although it will be hell at first. Also a very good ideea for a solo throughout the game is the monk. VERY powerful dude. I almost thought he was a cheat. Yep.. i lied. I did finish the game solo with a monk and found it too easy. Esspecialy ToB. And of course all the items you find are useless `cause the monk doesen't wear anything.
About your thief.. hide him in the dark and backstab.. there are some exploits i think will help you.