So I'm writing a story with a MC who is like an evil over Lord type he's like Apocalypse meets Darkseid. Anyway his love interest is his bounty Hunter. She is basically like a slave but her service is willing mainly because he saved her from a worse fate. Their relationship is like Pandora and the Hidden One from Sleepy Hollow, my characters they very dysfunctional in a 50 Shades sense. A common theme in the story is him being very ambiguous about his feelings while she's constantly bending over backwards for him while often wondering if it's one sided. I hint he does by having him do small things but at the same time he treats her no differently than any other in her job position.
Nothing about that is romantic to me but hey, Christian Grey is (somehow) a romantic hero for many people. On that basis, I wouldn't change anything. There's no way you can make this relationship not-disgusting for people like me, and it sounds like it'll appeal to all the people who loved 50 Shades. Which, I don't have to point out, is hardly struggling for sales.
I was just struggling with the same issue. I went back and added a "first date" scene for two of my characters. What a horrible slog. I hate going on real first dates trying to write one really sucked!
Hmm. How to make a romance more genuine? Have arguments, snidey remarks, throw things, say stupid things, do things they will regret, make them question their choices, have sex because they want to rather than just using it as a tool to attract readers. Was Christian Grey a romantic hero? I think he was just a man who knew no different. He didn't inflict pain and dominance because he hated women, he did it because he was taught to do it, he really didn't know any different and by the time he'd realized it wasn't considered 'normal', he couldn't change himself. But, from a controlling point of view, he tried to take control of everything in his life, and to a certain point, he did (having people followed et-al) but in the bedroom, he relinquished that control to the woman by giving her a safeword. SHE had all the control, SHE decided when to stop, when to go, when to push herself. So, was he a dominant, or was she the one testing the fairground rides before deciding which ones made her laugh and which ones made her sick? OK, I've gone off at a whacking big tangent there, I do apologise. Oh, rethink the romance lines. Too many 'melt the heart' moments will make a reader put the book down. Yes, you need them, just not in every conversation.
Romance is authentic if it's not perfect. I think that authenticity comes if the people involved know what makes each other tick, or are interested in fully finding out... What makes her happy? What pisses him off? Like if she loves pasta, but he can't stand it, and he makes her baked ziti after a hard day, etc... Things like that make it feel real.
You could always kill the bounty hunter to show him mourn. That demonstrates his feelings. I mean, seeing as you intentionally choose to make it this way, I don't get what your question is exactly. Do you want to change what you have or add to it?
When your MC won't express love through words, the easy alternative is actions. My first thought is to put the MC in a position where he has to choose between protecting the bounty hunter and furthering his own goals. If he actually loves her, he protects her, then acts all tsundere and claims he was just maintaining a resource. If he really doesn't care about her, he keeps to his goals and leaves her to bail herself out and rationalize it all.