Originally started to tack this on as an edit to my post above, decided to give it its own post instead:
Oh also, regarding your worry about what it will be like when/if she's wooing someone new, you can always ask her if she intends to continue to be open to new loves in the future, and how she handles splitting time and attention between old partners and new ones. Some people do get caught up in "NRE" (new relationship energy) which can leave their old partners feeling neglected. If that ever happens, you just need to speak up for yourself and make sure you're still getting the love, time and attention you need to feel cared for. It will probably involve a lot of discussions of how you each show and want to receive love, what your needs are, and juggling of schedules. Poly can be absolutely wonderful but it's not ideal for people who need everything to be neat and simple or for people who don't like to talk things out. Of course, that makes it ideal for lesbians, who are notorious for talking everything into the ground.
OSO = other significant other