Honestly, I'm generally not the biggest fan of photos in which you can tell that a man-made light source was used on the subject(s) while there is noticeable ambient light. That is, if the added stobe is so subtle you can't tell it was added, great, but otherwise it too often clashes with the ambient to me. That being said, I honestly liked the lighting here even before you said it was only the parking garage's own lights and not any additional strobes. Great, great find on the location, with that lighting able to illuminate them nicely from head to two, and great job on the timing, getting the nice balance between garage and outside lighting.
I really like the composition of this - never mind the couple, the location has such great geometric appeal. I think you played on that really well with the pose, keeping him very straight and square to the camera while letting her, as a nice counterpoint, curve and fold into him. The only nitpick I have is that his forehead is a bit distractingly bright. Not saying it's blown, even on my crappy work monitor I don't think it is, but a slight burn might bring the attention a bit more to his eyes and her face.