Rather than discuss with you why you are jealous and how to fix it... I say use it.
Use this feeling to keep you motivated to do the little things that make such a difference. Of course Miss Brattified has already started that ball rolling with her great post.
But the bottom line is this. Don't let it get you down. Let it push you forward. You don't want to bombard them constantly with things such as MB suggested but you do want to take the time to be a part of the family in every way that you can.
They say it takes 30 days to form a habit. If this is the way you operate for 10 months then maybe you will form a firm enough habit of showing your feelings that you won't be one of those guys who forgets how to do that after you get married.
I teach my son... keep the fire alive. It isn't hard to keep it alive but it is hard to revive once you let it slip away.
And sometimes it pays to count your blessings.
You have in laws that you WANT to be around. That isn't the case for everyone.
Will she be moving to where you are when you get married?