>>7642032
Look up how other artists do it.
You have got three options usually.
Disembodied cocks, this is when you mainly care about the woman's pose, usually use this for full nelson, blowjob focus etc.
Faceless male, bust up. Useful for groping, kissing, breast play, paizuri and other illustrations where you want the viewer to be more immersed.
Full bodied male, well, this might go better with a simple background to fit everything together. You usually bother yourself with drawing a male character to this depth when you have multiple girls interacting with him.
In your piece, since you have gone with a gloryhole like setting, disembodied cocks can work since the appeal lays in the anonymity of those standing behind, amplifying the female character's slut factor.
Adding more here would take away from the main focus, you may want to apply these ideas to another piece.
Or also not apply them at all, it is your choice.