Fed up with 'supposed best friend'
Do you feel upstaged because she's got married first? If they did it to get an army house, & with a baby on the way, well I can see why they would chose to do it this way.
You don't mention what happened between you & your fiance & that's fine, but do you think that your friends are convinced (rightly or not) that it'll happen again & your marriage will end in tears & they don't want to be a part of that?
If she feels that you've grown apart & will never get that closeness back though, it may be that you have to let this go. Its always incredibly difficult when friendships end but I do think that sometimes its for the best.