If you look for the tag "jealousy", there's plenty in the forums for ideas and such. You can start with the idea that jealousy is common and that feeling jealous doesn't make you a bad person. Our feelings are what they are; it's how we handle them that define who we are.
You also sound like you have some worry about security. As a poly male married to a mono female, it was really hard on me finding someone who I could trust to love and accept me. Her support means the world to me, and not a day goes by that I'm not thankful for her. Who's to say that your husband doesn't feel the same way about his loving wife?
In my experience, love isn't a zero-sum. Anyone else your husband may love can increase his total capacity for love, not detract from what love he already has. At least, that's what I believe.
Here's a very simple question: Have you told your husband in blunt terms that you need reminders that you're his #1? Us dudes sometimes need reminders of things that y'all ladies take as obvious. It's especially helpful for us foolish men if you also suggest specific things that remind you your awesome. (For example, I make my wife's coffee every morning though i don't drink coffee as a everyday way of saying she's special.)
Another idea: ask if he can schedule his nights out in advance so that you can have girls' night out those nights. That way you each have a fun night, and no one is at home on the couch obsessing too much.
Another thing you might consider is a jealousy-buddy (you might not use that term with the person, but you get the idea). In other words, have someone you can talk to (online, in person, or on the phone) that will let you vent when you get worried and will help keep you focused on how yummy you are.