Sexuality question

So since like 9th grade I've been questioning my sexuality. I've been with my boyfriend since then as well and we have openly talked about my sexuality. He thinks that I can't know my true sexual identity if I've never been with another woman. But I am extremely attracted to women sometimes. I also know that if I wasn't with my boyfriend I would be open to dating anyone (lesbian, bi, a transgender person, an asexual person, etc...) I am not attracted to someone based on looks or gender I'm attracted to a personality. I truly believe I am pansexual and I don't know how to explain to him that I don't need to be with anyone else to know this. Any suggestions?