Is she being selfish?

Ok so me and my gf have been dating for quite some time now and we've had sex and everything and it is amazing but I'm technically a virgin because I've never had sex with a guy and only thing me and her have done is fingered and recently I asked her if we could have a threesome and she got very upset got mad and started crying because she thought it would always be me and her I explained to her it still would be and that I was just curious as to how it felt because I've never experienced it (keep in mind she's experienced it and had sex with a guy before) so I'm stuck in this position now and idk I want to know do you guys think she's being selfish? Or am I just totally wrong for even asking her?