For us jealousy still rears its head from time to time. Much of it is that my girlfriend often feels we would 'be better off without her' and she worries that we don't need her. Which of course isn't how I feel. I want her, but I also want time with my husband. I want her to not feel angry at me when I'm with him or when he and I happen to get alone time (doesn't happen often, we have kids!). When he is with her I feel happy, I work hard to not feel resentful of their time, since I know the only person I can truly change is myself. I guess I practice 'compersion' in those circumstances, as much as I hate that made up word!
So, how do we deal with it? Talking, crying, hugging, making promises and keeping them. All the ways you would normally try to deal with jealousy in a relationship. We try to address the underlying insecurity that drives the jealousy, instead of the manifestation of the jealousy itself. That is not always easy, but we do try.
Maybe if you had a more specific question I could help more?