So I am supposed to be happy he loves her because it increases the love in this world? I love her so much that I can let her love someone else? That's how it works? How about people making a commitment and sacrifice so that what you have has value and meaning. Nothing ventured, nothing lost. Every story has at least two sides. Please try and see the other side.
To the first question: yup. To the second: also yup.
How it works is that you give up on thinking of this the way you do. This is not monogamy. The rule book you were taught has been tossed out the window. The values and virtues are somewhat the same, but created in such a way that they put the "self" first and others after. Not in a negative sense, as EVERYTHING is geared towards belonging, mutual respect, integrity, empathy/compassion for others and a whole lot more. There is no room, in my belief and from what I have noticed, in polyamory, for co-dependency: merging and folding into one's partner's life so that each is completely reliant and dependent on the other. There is only room for autonomy.
Do a search for the "Foundations" or "Lessons learned" threads, read them, and see what others think of how to make this work with a strong foundation. It does work and people are happy in it. There is a lot to learn, though.
The sacrifice you speak of comes when that little voice at the bottom of your heart still says that it is committed and still says it loves her. If you have this, then you will walk through all this shit to the other side. There is another side. If it fades, then you will still walk through it and end up without her, but alive still. You will live through this, and you will likely be a better man for it, if you choose to be, instead of bitter and resentful. That is your choice, but you will carry on, regardless.
The meaning and value to all this is that she is unhappy, and because you love her you want to help her to become happy again. That has huge meaning and value. The balance is in making sure that
you don't sacrifice everything in order for her to do so... that
you don't allow her to make you unhealthy by not being firm in your own boundaries.
Monogamy rarely touches the amount of work that you are embarking on doing, but if you love her and are committed, then you will do it. If she loves and is committed to you, then she will, too. Right now, that is what I would be working on finding out. The house, that is, your relationship, is crumbling to the ground right now, and I really think you need to find out if there is a reason to start building a new foundation. The old one is rotten and not functioning.
I asked if we could hear her side because I realize there are two. I have not heard any indication as to whether or not we will be hearing it. I know there are two sides to every story.
I have been here a long time. You are not the first to go through this. Please realize that I also have been through this, and that is why I am here-- to pass on what I know.
I completely understand that your world is turned upside down and that you are in pain. I have seen that in my own husband's eyes, and HE DID GET THROUGH IT! You can too, if you choose it.