I have read many times here that alot of people do need a bit of a transition time after coming home from a date with an OSO. So their energies catch up with them and settle into being with the other partner. But I don't think I've read much here about the moments when two part company as one of the heads off to be with someone else, except for when someone drops their spouse off and they process some excitement or feeling a little weird if it's new.
Do you two live together? I'm a little confused about who is your gal and who is your primary.