Monogamous people often dismiss the possibility of being polyamorous by saying “I couldn’t do that; I’m too jealous of a person”. While I have no idea how or why all of the people who say that experience jealousy, in my experience, that is a meaningless statement- the same as saying “I’m not leaving this room, because I’m sitting right here”.
To explain this better, consider what jealousy in these situations is often about: it’s a fear of a partner leaving for someone else. The fear, here, is that once a partner finds someone else they will leave you behind. In other words, it’s a fear that your partner is operating under the rules of monogamy- they are dating multiple people, but eventually they will have to chose “the one” to stick with, and they can’t possibly remain connected to everyone. In other words, I believe that it’s not necessarily fair to say jealousy holds someone back from being polyamorous. Instead, holding on to monogamous norms holds someone back from being polyamorous, by creating reasons for jealousy.
This puts the statement in a different light. What someone may really be saying when they say they are too jealous for polyamory is that they are too monogamous for polyamory. Which ultimately is just stating the obvious . But this is an important distinction, because I don’t think the difference here is feeling or not feeling jealousy- it’s a matter of what norms someone expects their partners to operate under.