There is a decent kiss at the end of the little mermaid that stayed in my mind for art refferance, however kissing seems to be as much a signature as any manurism. IE: everyone does it differently. Some use more toung, some hold their partner's head. some kiss higher... And it also depends on the type of kiss... romantic, flirty, lustful or making out.
As for how I refferance faces, I draw the gyst of the head, like a stick figure, then I draw a line from the eye to whatever I want them to look at. If you want vega to look at his lover, then draw a line from Vega's eye position to his lover's head. Then adjust the head and body accordingly. Actually physically going into the position helps with muscle stress and comfort.
My suggestion for this paticular picture is to propt Vega on two pillows along his back, arching him so that his shoulders, neck and head are upright. That seems like the most comfortable position. Otherwise, you could keep his position as-is, raising his chest a bit, (which will reajust the position of the head) and rolling the eyes up to make a sence of pleasure, as an alternative.
As for his lover, (sorry I don't know his name) He seems to be hovering on the body as if not actually between Vega's legs. Allow the fat on his chin to interact with Vega's waist, or even tilt his head straighter aligned with Vega and draw his lips conpressed on Vega.
That's all the help I can think of with positionning. As for the pants, I was taught never to actually use black as a colour. Use 80% or 90% grey to allow for shadowing. This will also help to understand what's going on down there.