How to improve your photo
If I have one issue with your photo, it's that the male subject is looking at the camera. For some reason, that makes me feel a little uneasy. I would like to see a frame where his attention is toward his partner or her midsection. I think that would serve to provide an intimacy that's missing as he eyes a third party.
As mentioned above, a little kick-light might work to separate the subjects from the background, but I don't miss it. The simplicity of your lighting is one of the things that makes this portrait special.
I would also liked to see just a little more space around the couple - it might serve the intimacy thing again. Not a lot, just a little. Honestly, though, there's three boxes for the critique and I feel compelled to fill 'em. There's nothing wrong with your composition!