engaged to a man, want to be with women

i'm bisexual, ive never been with a woman though. i'm in a long relationship with a man, were engaged. i love him sooooo much, he's my best friend. but i really LOVE women. i realized i was bi after i got with my fiancé, all the signs were there but my family is super religious so i doubted myself. but now that i'm with somebody i really love and want to be with, i feel like i missed out on women. i just really want to feel what it's like to be in a relationship with a girl but i dont want to leave my fiancé. he's TOTALLY down for a threesome (of course) but i also want the intimate parts, not just the sex. idk what to do /: