Originally Posted by pandaramone
. . . he is my first lover, and relationship, and these are added factors that complicate things.
It only complicates things to the degree that you tell yourself it complicates things. The fact that he was your first sexual partner and this is your first long-term romantic relationship, doesn't have to complicate anything. How do you let it complicate making choices for yourself? Yes, these are significant "firsts," but you are adding additional meaning to the facts that do not necessarily need to be there.
Really, so what if he was your first? You are unhappy and crying because you don't like that he has other relationships. Does the fact that he was your first mean you have to stay? No. If he were beating you, you wouldn't. If he were ignoring you or a criminal, you wouldn't. Not to say that his practicing polyamory is comparable to those things, but it does not satisfy your need to be monogamous with someone. Sometimes the most loving (and grown-up) thing we can do for ourselves and the ones we love is to let go and move on. It sounds like it might be time for that. You don't need to endure heartbreak just because he was your first lover.
I know how it feels - from the age of 16 to 19 1/2, I had a very tight relationship with a boy my age. I thought it was the be-all and end-all of relationships - he was my world. But at 19, I realized I needed to experience more out of life, and to break free of his extreme jealousy. He wasn't my first sexual partner nor my first relationship, but he was the first person I wanted to marry and the longest relationship I ever had until I actually did get married 20 years later. I loved him deeply and I had to break up with him. It hurt. I told him, "We've both been growing up but in different directions. We are on two different paths and I will always love you but I need to follow my path." I was scared to break it off, but I was also brave, and I never regretted it.
There will be more lovers, and there will be one with whom you can create the sort of relationship you truly want. But that can only happen if you take action and create the space for it to happen. The world is full of so much love. Be brave.