Redsol: probably the best advice I can offer is that you keep communication open. As a new relationship, there is a strong impulse to share a lot, and that can go too far, so try to balance honest openness against eager pushiness.
I worry when you write that you feel put out by coming in second or third. You're the new guy, so it's understandabke that your aren't in tge same position. Where you stay or go in thise terms is something you'll have to work out with her over time. Patience is also as hard but as valuable as honesty with poly relationships.