Don't judge

Okay so I consider my self a heterosexual female, I've always dated guys, had sex with guys, been attracted to guys etc. I let my fiancé 2years ago and were happy, have a great sex life all that. But since I was a teen I have been really interested in hooking up with a girl. No dating really just having sex with one. Before I got with my currents fiancé I actually made a tinder to match with girls but I never met up with any. How to I tell him I want to have sex with someone else (a girl)?! I want to hook up with her first then later let him join if I liked it. Opinions pleaseeee