Jealousy’s a thing we talk about a lot in poly. There are some people who genuinely don’t seem to feel it, but most of us? We’re human, we get jealous. Even if we’re monogamous, even if we don’t have to process our partners actually having relationships with other people, there’s usually some way that you have to share their attention that you have some feelings about. Whether it’s about friends or work or their hobbies or Christina Hendricks or even just the idea that you could be losing touch with them. Jealousy’s not a good thing, it’s not like in Twilight where “ooh, threatening murder over me is how he shows he really loves me!”, but jealousy is not evil. It’s just an emotion, and how you express it makes the difference. Bottling it up until suddenly you’re really upset and you get into a big nasty fight: that’s bad. Bottling it up forever to try to be the Perfect Undemanding Totally Chill Partner and eventually your head explodes: also bad.
So just say it. Just lay your emotions out there on the table so you can work on it together. “I feel lonely (or neglected, or jealous) sometimes when you do X, and I would feel a lot better if you did Y or reassured me about Z.” Like everything you’ve got to do this in good faith and have some flexibility - you’re getting into some real bad-news territory if you ask your partner to never make you jealous about anything ever - but there’s a lot of things in between that and totally stifling yourself. Sometimes you just need to hear from them that you’re not losing them. Sometimes you can make compromises like “going out to dinner with your ladyfriend is fine, but you’re going to owe me dinner next week,” or “okay, you can watch Mad Men, but no freeze-framing.” There’s just a lot you can do when you talk about jealousy before it’s a crisis.