"Anyway, sorry for talking about sex so much, I can see it's not helping your problem, is it?"
You are embarrassed that she has again noticed your hard-on.
"And I know it's always hard for you to go a few days without, so this must be really difficult for you!"
You agree, but tell her that you'll be able to get by. But you also say that you wish she wasn't stretching in such a sexy outfit and talking about all these dirty things.