need HONEST opinions

OK, so FH I & met in HS, although we did not start dating until 4 years ago. His 10 year reunion is this month & I have recently put on a bit of weight. NOW, both my ex & his ex are going to be there, neither one of us has seen either one of them since HS, but I gotta be a BEECH & try to look slamming. Problem is I gained 15 lbs in the last 3 months. I am totally dieting, but I don't really know how to dress & still look good?

Any suggestions?