I can sympathise. I'm still friends with a group of people from my sixth form college and I see them whenever I can. They are the most kind, supportive and non-judgmental people I've been lucky enough to meet (we've all been friends for nearly 10 years now). With my friends from school, I had many chances to get in touch with some of them again but I always chose not to because of how differently our lives turned out. We all got similar grades at school - then most of them did 3-year degrees straight out of school and are now earning an income, are in stable relationships, even looking for their own property. Some did Masters degrees and are getting promoted in their fields. Whereas I got kicked out of uni after 4 years for failing one exam and have now started all over again from scratch in another country. I'm sacrificing many more years of my life - including age, relationships and income - to keep pursuing what I want to do. I look back and think about how far behind I am in my own life compared to all my former colleagues, and the fact that in total (by the time I am done), I will have spent 4 times longer than they did to get a similar salary to what they are earning now. Even my former uni colleagues have all finished their degrees and are earning in half the time it will take me. NGL, that does upset me sometimes. So I have to train myself to forget about what happened in the past and focus only on my present and future.
It's hard not to compare yourself with people you went to school with and who you are friends with. The most important thing you have to do is focus on yourself and do things that make YOU happy. You don't need validation from anyone, and if anyone is giving you judgmental or patronising comments they need a square punch in the face. But if these people are genuinely good friends with you, they will support you no matter what. Through whatever hardships you may be having - maybe you don't like your job, maybe you're fed up of being single, maybe you're not feeling as healthy or as motivated as you used to be. But it definitely helps to have someone to talk about these things with.
When you talk about your issues with your friends, you'll find out that things aren't as easy for them either. Some of my friends from college may be earning now, but renting in London is still way out of their budgets. I may be envious that they still live and work in London (our home city) while I'm away for the next several years but living has become problematic for them. Everyone has got their own insecurities about something. Whatever it might be, talking about it and sharing everyone's problems brings people closer together. If you don't feel comfortable talking about it with your friends from school, ask someone else. Parents, family, work colleagues, significant other etc. If not, therapy and counselling!