Would you happier if the guy were objectively super hot, smart, rich, successful, funny, interesting? You wouldn't feel jealous/threatened?
What if he were super sexy but seemed like an asshole?
What if he were completely similar to you, almost like a clone of you? In that case, would you feel like you understand what your wife saw in him, or would you feel threatened/bothered that he's so similar to you?
What if he were the complete opposite of you, and had qualities you lack that you wish you had? Would you admire your wife for finding someone like that, or would you feel threatened?
This is food for thought so that you can try to identify what's bothering you.
Maybe you are just not happy with a poly marriage? How did the opening up process go--whose idea was it? Do you feel like it was forced on you, or that you and your wife rushed into it? Do you struggle with the concept of polyamory, or are you excited to try it? Have you been on dates yourself?
For my perspective on what your wife might see in her new partner: I spent last year dating a guy (Rick) who might objectively be judged as a "loser" by some people. He is very overweight, struggling financial, and has some physical and mental health problems that prevent him from doing a lot of things that other people do easily. He also has very low self esteem.
He shares a lot of obscure interests with me and we had some of the most interesting conversations I've ever had. He is a fantastic kisser and we had the hottest makeout sessions I've ever had with anyone. He has some interesting sexual compatibilities with me that allowed me to explore some aspects of my sexuality that I had never gotten to before. (And his dick is pretty awesome too!) He was deeply appreciative of me and thought I was the hottest thing ever. He was kind to me when I was going through a difficult time, and gave a me a new perspective on a few emotional things. He is open-minded and passionate about politics. He is caring toward his family of origin while not wanting kids of his own (like me).
But none of that would be visible to someone who met him--they would just see someone with a lot of challenges and wonder what I saw in him.
Keep in mind that it's also possible that your metamour is nervous around you and isn't able to be his best self--maybe he is funny and interesting normally, but feels too shy and awkward around you to demonstrate his true personality.
When someone senses that they aren't liked, it can make them even more awkward and closed-off, increasing the other person's dislike of them. It's a hard cycle to break. He can probably feel you're judging him.
On the other hand, I understand what it feels like to be appalled at your partner's choice of other partner. My relationship with Eli ended in part because he fell in love with someone whose behavior and attitude appalled me. Even with his relationship with her blew up (due to her appalling behavior, of course), I couldn't see him the same way and had lost a lot of respect for him.
But...it doesn't seem like your metamour is actually doing anything to deserve you to be appalled?
Is it just the idea of your wife having sex with someone you find physically repugnant that is so off-putting to you?
