Let me ask...you've known and been friends with them a total of 3 years? And it has taken you well over 2 of those years to become committed to the poly relationship?
So, if the answer to those questions are yes (that's the way I interpreted your post but asked to make sure) then, things are going to be different than the fun times you had together for over two years. You have changed your thinking. What used to not have bothered you because you weren't committed now may be a concern for you.
Ok, as an example but fully knowing I don't know much...say before you committed to the relationship you knew they had dates, this didn't bother you because they are married and that's what they should do. You didn't really want, or admit to wanting, the same for yourself. Didn't think you deserved it or that you should want it. Now, you are committed to them and you love them and he is your boyfriend. Just as a relationship with one's wife demands certain things, or wants certain things, a relationship with one's girlfriend does the same.
You and Sea are adjusting to the fact that you both have certain rights. Some of the same rights. While it may have been said during the 2 years plus that you didn't commit that this was wanted, the reality of things is different than what one imagines about such a relationship. (Well, the reality of almost everything in life is different than what we imagined it to be.)
January will make three years since both couples of our quad met each other. Someone at our poly meet and greet last night said that we were obviously making poly work. That gave me pause and something to think about. Well, shit, we are making it work. We may have finally figured out what makes it work for us. Gotten some of the big kinks out but it will always be a work in progress. How long did it take us to get to this point? Over 2 years. Did I/we all have feelings like you have described in this post? Absolutely! Which is why I can empathize with you so much.
I suppose you have to do something along the lines of decide...yes, I am going to do everything within my power to make this work. I need to get that confirmation from my partners as well. Communication is paramount. However, the truth of the matter is that everyone doesn't communicate the same way. Figure out the best form of communication for all of you. Then do your best to make sure you try to communicate the way each of you needs. That way you will better understand each other. For example...Sea may not respond well to bluntness...in what different way could you say the same thing that it doesn't make her defensive?
Ok, I'm finished. I don't have answers usually. Just more questions for someone.
I wish you all the best of luck and I do empathize with you all. I've been in all three of your shoes at one point during this relationship.