It seems counter intuitive to take walk breaks while training for a race. Are you practicing going slower? Shouldn't you be pushing through the pain?
I've spent many years running long in the mornings, and while I'm not the fastest runner on the planet, I do have LOTS of experience. And I prescribe to Hal Higdon's advice:
"Walking is a perfectly acceptable strategy even for intermediate runners, and it works during training runs too. While some coaches recommend walking one minute out of every 10, or walking one minute every mile, I teach runners to walk when they come to an aid station. This serves a double function: 1) you can drink more easily while walking as opposed to running, and 2? since many other runners slow or walk through aid stations, you'll be less likely to block those behind. It's a good ideas to follow this strategy in training as well."
Since I use a water belt for my long runs, I tend to take my walk breaks at stoplights or at street crossings. It gives me the chance to take a sip of water or bite into a Skratch gummy or two while I am not bounding down the street. It also teaches my body to jump from a higher heart rate to a lower one and then back again. It gives your body a chance to rest and you'll be able to run longer distances with short walk breaks.
Higdon is spot on when he says "It's best to walk when you want to, not when your fatigued body forces you to.
So get out there and try and run just a little bit longer next time. It's okay to walk. And it keeps the group happy too. When you take short breaks, your running buddies can regroup and enjoy the run together, sharing stories and getting to know each other a little better. And that, my friends, is a good thing.