I've read that people are more jealous in a relationship when they feel insecure or vulnerable. And I've discovered that it's true at least for me. (I never was jealous when it came to my ex-bf, because he never gave me reason to feel insecure when it came to us.)
And them being your new "addition" makes your hubby probably feel insecure, because it is a new relationship. And trust isn't built in a day, or a week. Even if you say you trust someone there are probably moments you doubt them.
Sometimes, though, you just have to trust people, take their words first in order to get something back. Yes, unfortunately that also means that you can land face first in the mud.
Maybe you could ask him how he would feel if he were in their shoes? That is, if you haven't done that already.