You need to go to a save earlier where you didn't have black heart with Gunnar.. if that's not possible then you're unfortunately stuck with that.
I don't know about bandits for that quest, I never got the quests from the receptionist because I was hired at the brothel, how? You need your skill points somewhere around 18-25 I guess and have lots of sex experience (I'm a bottom who is 'loved' by a lot of enemies)