Absolutely, Sterling should be present. That's what I meant by DP (double penetration), but I see how my sentences weren't clearly connected. The thought of Sterling and Drew high-fiving as they spitroast Keira (or whoever) sounds fun to me.
I think I wouldn't even mind if Keira or Nora wanted to bang Drew without Sterling present, since they all had a past together, and Sterling doesn't seem to have a particularly strong attachment to them. Such scenes would be sort of pointless to the central fantasy of the game though.