NOS,
That sucks. The only thing that comes to mind for the sudden change of attitudes is the fact that you are getting married. It is a major life status changes, and your friends may a) feel left out, b) feel like they are missing out, especially if you are engaged to someone they admire as an individual, c) feel they are loosing you and your hours upon hours of devoted friendship to someone else, or d) all the above and then some. OR, don't discount that you are going through a lot yourself... whether your friends are aware of it or not, your emotional "home" is changing...
I noticed another thread, by Aztec, where someone mentioned that guys don't talk about feelings. It sounds funny but it's true. I have a particular friend who has stood by me in some pretty difficult times; but I tried talking about feelings once with him and he changed the subject 3 times back to cars and projects. I got the hint, and never tried again. When we go our seperate ways for a while, I just leave it at that... we eventually get together again and have a lot of catching up to do (about things). So, don't always count on trying to talk it out and figure out what happened.
I believe you will soon find many married couples that have gone through similar experiences and will be able to build some new friendships based upon a different level of "commitment".
Congratulations ! I wish you well.
ugly