Your mind wants to “protect” you it sees getting in better shape as a threat. If left shine the subconscious will run wild trying to get you to stop.
One suggestion is meditation. The more in touch we are with understanding our mind the easier it will be to manage these moments.
The second suggestion is to come to with a plan. When you see someone else, in your head or maybe even to the person congratulate them on their success. Be happy for them. Grateful that you have something to look forward to in your own process. You can’t feel gratitude and a negative feeling at the same time. Even if you don’t do that just have a plan to help change the routine. Decided a shred of time what you will think about our day to yourself. Stick with it and don’t forget to reward yourself when you do. A good reward might be an extra 10-15min doing exercise (getting you closer to your goals ) or maybe invest in those new headphones, sports drink, or water bottle?
Give it time. This is your story. You don’t know what they’ve been though or haven’t been through. Focus on what matters most. You , I hope this helps 😊