Honest advise?
Similar situations for me, making excuses to avoid being around friends, families and others due to my excessive weight.
At first, I also felt "guilty" until I learned the excuses I made to friends and family were simply lies. The reality was the guilty feelings I was experiencing where more related to what I call the "self-preservation mode to avoid embarrassment and shame". Why did I feel embarrassment and shammed, I can probably write half a book just on that topic alone. There is a good write up in Psychology Today that discusses the similarity between feelings of Guilt, Embarrassment and Shame, I would say it's recommended reading for those who are morbid obese.
https://www.psychologytoday.com/us/blog/the-pathways-experience/201709/embarrassment-guilt-and-shame
Battling excessive weight goes far beyond "eating less and excising more", there are many Psychological related factors that MUST be addressed or your chances of successfully loosing weight and keeping it off will be reduced substantially. The lies, specifically to yourself have to stop. Perhaps if you told your friend the REAL reason why you did not want to participate they would be more understanding to your weight situation? And if they are not, I would say perhaps it time to surround yourself with new friends.
When you say "I feel like no one can relate", I find that hard to believe, this forum is FULL of people who can probably relate to your situation in one form or another. You have already taken the first step by posting your message, never be afraid of asking for help, within this format or professionally.