Need some advice in dealing with a friend

Hi everyone.  First time poster and new to the forum so if a situation like this has been posted before I'm sorry.  Here's the issue:

I've been with my boyfriend for the past 4 years.  My friend has been with her boyfriend for 5 years.  We hang out with a large group of people and we are the only ones who aren't engaged or married.  My friend and I both want marriage but our boyfriends have their own timeline.  We share a close bond because when people are talking about marriage or their engagement we laugh and joke how we've been with our SO's longer than most of them have been married.  Her boyfriend has made references in the past that he doesn't plan on proposing until 2010!  Recently, my boyfriend has taken me engagement ring shopping and I know that the proposal is coming soon!  Here's the problem - I know that when my boyfriend does propose, I am  no longer going to have that same bond with my friend.  Also, I know how it feels to want to be engaged so badly and have a friend announce their engagement and can't help but be a little upset about it.  Of course you are happy for your friend, but also sad that it hasn't happened for you yet.  I don't want to cause any pain or anomosity between me and my friend.  I just don't know how I'm going to handle this situation.  Anyone had to deal with a situation similar to this?  Any advice would be helpful! 

[it's good to be good to people you don't understand]