Warn her

You squirm in pleasure from her oral ministrations and gasps as you feel your orgasm approach, "Olivia...I'm nearly there."

She looks up and slides off your cock and strokes it quickly while your squirm on the bed. After a moment, she looks confused " Is this righ-"

Suddenly you groan in pleasure and your cock throbs excitedly in her hand. She jumps in surprise as the first burst of semen answers her question and lands right on her face. Followed by a second, third and fourth. The fifth dribbles down your shaft and onto her hand and she starts slowing down her strokes.

You look at her in surprise. The semen dribbling down her face looks almost cute as she looks in shock at what just happened. You think for a moment that she might be angry until she grins and giggles. "I guess that answers my question." She examines the white sperm on her hand and plays with it a little between her fingers, "Its weird though...and warm"

Still having the occasional shiver of pleasure from your cock throbbing weakly, you manage to gasp out a simple "Uh huh.."

She stands up and wipes her face off. "well...I should go before my parents suspect that I'm not being a good girl...Maybe" she stops for a moment before continuing, "Maybe sometime in the future we can do more...See you Monday"

"Y-Yeah...Maybe. See you Monday" You relax back against your bed enjoying the afterglow of your blowjob for a few minutes longer before heading down and rejoining the party.

It would seem that the party has nearly reached it's end. Dean and Emily leave shortly after and Natalie after that. It would seem that overall the party was mostly okay...despite what happened between Natalie and Olivia.