OK, you have my attention. My +15 Ref save is a little weak since my druid levels and my PrC levels don't have good progression in REF, but for a fireball, I am just fine.
My friend the monk just twigged to your casting as well. He and I have played this game before. He Abundant Steps both of us next to you while I draw the rapier of puncturing and cast haste. You want to respond authoritatively because we are getting ready to flank. Sure, my 3 levels of rogue only give me +2d6 damage, but with three attacks/round + haste, you are looking at 2 jabs and a puncturing attack for my 3rd attack, then another jab. The monk will probably flurry of blows you, and then for the hasted attack, he will look at a Stunning fist. After all, your Con probably just dropped by several points.
Of course, this is assuming that we even have a chance to get that far into the combat. Between the Ranger (archer path), the Wizard, and the Druid, your fireball might have received some pretty hefty return fire.
Of course, we are all 16-17th level. If you only fireballed us, you were silly.