Hi,
Sometimes just being around people who are positive and upbeat will help you to feel better, I know that not being on the same level as them right now is hard to cope with, making you feel probably worse than you should. They will not always remain on the up, life just does not work that way.
If these people are your true friends they will understand what you are going through. Sometimes I look at people who seem to be having all tthe good things in life and try and figure out what has helped them to get to where they are, then I try and change the things I can.
People should like you for who you are not what you have, and you have probably been a support for them in the past, which is something of great value. Look at yourself and try and see what you have done for yourself and others, can your friends say the same thing?
I'm sure behind all the presented happiness of your friends there is also problems in their lives, they just don't want to show it,for the fear of looking bad(Maybe??)
I don't know if this helps much, but keep us posted on how you are doing and don't be so hard on yourself o-kay
Take Care of Yourself