This is my first real relationship and I can't help but feel that I've missed out on a part of myself because of it.
FOMO, particularly when you're young and at your attractive/horny peak, isn't unusual. I definitely felt this way in my first long term relationship (only two years at the time). But it does cut both ways. Moving away from an SO can create the same sense of indecision, frustration, and longing. Not being able to have it all is something young people struggle with.
Recently I've been coming to realize that monogamy has never sat right with me, but when I brought this up to him he immediately shut it down and made a comment about poly people just wanting to cheat.
That's not an unfair take, given my anecdotal experience. I've seen more than one divorce start with "let's just open up the relationship". If he's got personal experience with this (family or friends or a prior SO who broke up this way) the anxiety isn't unusual.
At some level, you have to seriously ask yourself the question of who you want to spend your time with. You can't cling to an old SO while juggling a new romance, particularly if the two people in your aspiring poly relationship don't want to be together.
Cause that's what this really boils down to. Not who you fuck, but who you come home to.
On the plus side, if you're young and you are still experimenting with your feelings, you've got time to make the wrong decision and recover.
On the negative side, experimenting can be painful no matter which way you go. Ultimately, you have to recognize that other people have their own needs, and being in a relationship isn't just about what you want. Whether that draws you together or breaks you apart is contingent on compatibility. But trying to split your time and your love between people who don't share those feelings with one another is dangerous and difficult, and prone to leave everyone feeling badly.
Given this guy's track record, $5 says it's literally nothing. Just rumors and suspicions woven together into a speculation on vast conspiracies.
If it goes past "we found an IP address had touched our servers registered IN CHINA and now someone in China is doing things with a computer that only we should be able to do!!!" I'll be legit surprised.
But I'm not going to bother researching enough of this to find out.