Eko, thanks for coming here and telling your story. We'll do what we can to talk you through this.
Your situation is quite typical - one member of a previously monogamous couple suddenly realises that they are poly, either due to a revelation, or due to meeting someone. The other partner knows for sure that they aren't poly and that this person is their "one and only".
You don't understand how his mind is working, and the stuff he is saying sometimes makes it sound like it's in a foreign language - except you understand the words but they don't make sense. Am I on the right track?
Some couples go through the immense pressure of trying to keep things "equal" by pressuring the monogamous person into being poly. That very, very rarely works, and often causes a lot of resentment and pain.
So, if you are certain that you are monogamous (and it sounds like you are), and he is polyamorous (and he is at the start of this journey, so he may not know everything about what he wants), then you need to start by accepting that fact about each other, and understanding that sometimes stuff just won't make sense, but because you love and care about each other and because you are committed to your relationship, that the other person is telling the truth of their heart.
Being poly means not having to choose simply because they acknowledge that they are in love and want to be in a relationship with more than one person - and you are one of them! it in no way means that he wants to leave you, or "upgrade", or that he is unhappy with your relationship - quite the opposite, maybe.
The main idea that poly folk have that is hard to grasp is the concept of a capacity for infinite love. Some people say that for poly folk, love isn't a "zero-sum game". Put in English, it means that just because he loves someone else, doesn't mean he loves you any less - the heart has a capacity for infinite love.
I don't want to write any more right now, because I could ramble on and on, and it may not be stuff that you want to hear. So how about some feedback - am I on the right track with some of the stuff you are saying?
If you want credentials - one of my relationships is a mono/poly relationship - I am the poly part. We went through the transition from monogamy to mono/poly and had many hours of discussion. You are far from alone - there are plenty of folks who have been through similar can can talk with you about this on this forum.
"Listen, or your tongue will make you deaf." - Native American Proverb