When it comes to BL or GL, things of that make, I've noticed a strange disparity between the two. The female couplings don't involve as much violence (in my experience) as the male couplings do. Again, this has just been my experiences with the genre and yes, often the violence of the relationship is played as being 'hot' rather than concerning, in many instances. I've never done any kind of research into how many females write BL versus males and vise versa for the GL genre though so, hahah I have no solid numbers in that regard.
I think if you just write a good relationship in general (whether it has rocky moments or not, and whether it's a same sex couple or not, and whether you're inside the GL/BL genre's or not) if the skill is there and it's not being played off as something it isn't, (ie. Elizabeth pretending Azil and Karadur's relationship is 'romantic') by virtue of bad writing, then you could write just about anything. I'm a firm believer that there should be no limits to expression. To that end, I love complex relationships that evolve and or devolve over time and that eventually there will be a conclusion (even if it's not one I like lol).
I've actually written a character who is volatile and emotional, full of greedy emotions and cruelties. I also show that it's not something that is pleasant or some form of 'love' for anyone stuck being involved with him. I wanted to be honest about the kind of person he was, and all the people around him recognize him as cruel. By creating a character like him, I also have the chance to explore what brings people to these points, and where they can find redemption or sink further into the pit depending on how they experience the world. That's where I think distinctions become important: rather than selling a false idea that abusive tendencies are love, I want to represent them in the dark light they truly are and explore aspects of the human condition. It's hard to get it all completely right in the first go (and that's why editing and second drafts were invented lol) and ultimately it still falls to the hands of the agent reading the query as to whether or not a portrayal is published.
Quite the ball of wax, isn't it?