My bestfriend wants me to be her first?

we've been friends for about 20 years shes straight and definitely loves her men(muscle bound masculine) ever since ive known her shes always been boy crazy me on the other hand am a lesbian i've known i was gay since i was 12 years old shes the first one i came out to she was cool and open and accepted me for me, shes engaged now and getting married in a few months, the other night we went out dancing and to get a few drinks some guy was trying to talk to me so she was my bodyguard(which she always is every time we go out) the guy wouldn't stop so she tells him im gay and that we were together and then she kisses me (i mean really kisses me! ) shes never done that before ever even when i joke about her shes like naw strictly d***** but lately shes been throwing hints that shes "curious" she flirts and touches me in a certain way now(which shes never done any of that either) shes getting married soon plus i really don't feel comfortable being an *experiment" especially with her i mean after all these years now she wants to "play" what should i say without hurting her feelings