Lesbian Fantasy??

The other night my husband and his friend and I were drinking and somehow we got on the topic of a threesome. My husband basically gave me permission to bring another girl into the picture but says no way in hell about another guy. Well I have never went any farther than a girl fingering/kissing me way back in the day, so I don't think I would feel comfortable bringing a girl into our sex life for a three some right off the bat. I would love to be with a girl all the way and it's been a fantasy of mine, but maybe by myself first? Should I tell him that? Or just forget about it altogether unless he brings it back up??