fucking my bestfriend

so i had a talk with my boyfriend and he said it would be fine if i had sex with another girl, one in particular i had in mind was my bestfriend. She’s a lesbian and i’ve brought it up but i’m scared i’ve made her uncomfortable by bringing it up. She said she’d fuck me but she’s just insecure and she said to wait a couple years, i can’t tell if she’s saying that cuz shes uncomfortable and doesn’t want to or that she actually is down. what should i do?