Replacement

Recently I've been struggling with this question: what is the appropriate way to act when you feel like you're being replaced?  What's the proper balance between acting like everything is okay but also conveying that you don't like this?  Part of me wants to be happy for my friends.. happy that they are meeting and spending time with other people.. and I am.  But why does this have to come at the cost of our friendship?  I partially hope that maybe this time with new people will make my friends appreciate me more -- realizing how much of a deeper connection we have than they do.  This is a very selfish wish.  If only we could express how we're feeling to each other as easily as it is to feel it.