Yes, you probably need to do a lot of talking. Make sure you know where you stand.
The way I see it, she's told you how she stands, you need to figure out your place now.
You seem to be of two minds: one, you don't want to live without her, and you want her to be happy and be herself. Two, you don't think you could share her without being unhappy yourself.
The important thing would probably be to know what you have a problem with. Is it the idea of other people having sex with her? If so, do you know why? Would it be better with some limitations, for instance specific acts, or meeting the other people first, or the opposite, not hearing about it?
Are you more afraid that it would diminish you? As in "why am I not enough?" If so, that's probably going to be rather hard, but it's possible to work through. See, if you're mono-wired, as seemed to be the case, you work in a drastically different way. It is hard to think about things from her perspective, but I assure you wanting to be with other people doesn't take away from what she has with you any more than wanting to have more than one friend.
There IS the possibility that you don't fill her needs, that you are "not enough". Why? Because you're a single person. Imagine having just one friend. No other friends. Surely that person would be "not enough". They wouldn't fill all of your needs, because it's good to have several friends who are all different in many ways, be it personality, tastes, activities they like, etc. This is similar.
Now, another thing that people have raised is whether she is a swinger, or polyamorous (or I guess both). Is she looking for just sex? Or is she looking for things that include but aren't limited to sex?
I find it's easier to say "I want to have sex with other people" than "I might fall in love with someone else... But I'll still love you". Because people often can accept the idea of having sex with other people more easily than the idea of loving other people in a romantic way, so it hurts them less.
As a result, it's hard to be sure if she said it that way because she feels you'll understand it better, or if she isn't interested in other romantic relationships and is simply pursuing sex.
In which case, said sex wouldn't be the same as the one she'd have with you, due to the connection she has with you. It would be casual or recreational sex, and quite different, and therefore it also makes sense that you wouldn't be able to provide that.
Please keep us informed after you get to talk to her. And good luck, I realise it must be hard for you, since it's not something people tend to expect so it must have been quite a shock.