I think you have to be thrilled that he was so excited by what you did, and comforted that he has a stepmother whom he enjoys. He also tried to qualify his remark with "Well, maybe you're as awesome as her" which means, on some level, he knew he didn't want to hurt you. And the grass is always greener on the other side of the fence, especially when the other side of the fence is only visited every other weekend when it's party time at Dad & Kristi's.
I know how much it hurts to hear that someone else is even cooler, but look at what he's reacting to: Sierra Mist and dessert. And if the mom who gets them up for school every day and makes them do their homework and does their laundry and does the carpooling and the reminding and the lunch-making gets an occasional vote of "coolness" for a pizza night, that may put you ahead of the game in many moms' books.
I'm a stepmom and a mom, and I can tell you it's very hard to be either one. Stepmoms often have to deal with moms who are jealous or resentful of the weekend/party status, and stepmoms also have to try to reach kids who aren't happy that Mom and Dad aren't together. The stepmom (and dad) are also hearing stuff like, "Mom lets me do that" or "That's not how we do it at home" (making it clear that Dad's home is not really "home"). So they're probably being hurt by things "out of the mouths of babes" too.
And as a mom, we all worry that we're never going to measure up on the coolness scale to stepmoms or friends' moms or the babysitter or the scout leader or the baseball coach. The "ordinary", everyday, discipline-dispensing and routine-enforcing parent is often the one who gets no compliments, no credit for things that go well, and plenty of blame for things that go wrong. Eventually, these kids grow up and either miss you like crazy when they go away to camp or come back from college with a new appreciation of all you have done.
If you can get yourself to the point of being happy that your children have someone else to love them, that's good, and it comes from a place of confidence and self-assurance that you are strong with good values and a good head on your shoulders.
A lot of us can say we didn't appreciate our parents until we became parents and saw how hard it was. None of us thanked our parents as much as we should have or appreciated them at the time.
The less you can be hurt, and the more you can bounce back and say "Look at the awesome moon", the happier you will all be in the long wrong.
Hang in there.