I believe it's called either heteroflexibility or polysexuality. However, compared to our (pretty mundane) world, FR has a whole additional dimension to it - species. Specifically, sentient ones. If he somehow managed it with a cambion, an affair with a male dwarf berserker should be "almost straight".
The cambion in question is a succubus, right? Whose whole deal is that they transform into what people find most attractive? And since he refers to that cambion as "she," his relationship with her is basically the equivalent of him falling in love with a human woman. (Assuming of course that she didn't use her succubus-magic to magically seduce him)
