There's a difference between gently avoiding the exclusivity talk and going into a relationship knowing you never want to have it.
Blurting "I want to see other people" over first date calamari can come off as dismissive, so wait until it feels natural.
It was jarring to find out that our great aunt had basically spent her youth as the whore of Babylon. You're going to date Veronica _and _her best friend A lot of my friends, male and female, followed this kind of "Medieval Courtly Love, With Blowjobs" model well into college, like knights and ladies with bitterly divorced parents.
The situation can be a minefield, so here are a couple of ground rules for being an ethical he-ho.
If a woman is dating more than one man at a time, she is not giving enough time or effort to finding out if she is truly compatible with any of them.