Since he's bonded it doesn't affect him as much. Think about it, the suppressants work quite well on him because he's bonded and only if Robbie is close would the heat get worst. He was able to fake being a Beta due to the bonding and was living a pretty normal life. The Omegas have a hard time because they're releasing a lot of pheromones at once and need an Alpha to calm it down. Once they're bitten they can handle their heats quite well.
This story is just amazing. The way the author describes everything and the depth of it all, made me love it. I can't wait to see how the story will end and thank you so much for sharing with us such a beautiful and heartbreaking story.