He can't leave his vessel. If he did, he would have to wake him and ask for permission to inhabit him all over again. It's not impossible, but it's definitely something he'd need to talk over with the human soul first. In the meantime, his own Grace should protect his vessel's body and soul, but there is a very physical reaction to the building sensuality. When he moans in the back of his throat, the sound comes from his vocal cords, but there's an echo in his celestial body, an unearthly, delighted whimper.

His knees go a little weak at the feel of the other angel's Grace so close to his own. The power to break him from the inside out, the intention in contact nearly the opposite of that. He has to sink down onto the rocks lest he fall, and he tugs at Lucifer's sleeves gently, trying to get him to lie or at least sit down with him.

Unless, of course, having Balthazar on his knees in front of him is more convenient, ahem, for some reason. The younger angel looks pleasantly dazed, drunk with sensation.