Perhaps someone needs to give you permission to be able to feel like you dont' want to deal with everyone elses "happily ever after" right now.
Please do not feel as though you have to feel happy for everyone else, you really don't. I am sure in your heart you are happy for them, but you need to put yourself first and foremost. You have been through a hell of a situation and to have the pressure of being happy for others on top of that is a lot.
It's alright to acknowledge that other peoples good news makes you feel like shit right now because you are dealing with grief, betrayal and trying to find your way in a new life when you never thought you would have to. It is actually ok for that to be how it is.
I always thought I'd have kids, never did. Always thought I'd have a husband, never happened (there's time i suppose but still, i wanted to be a young bride). I alwasy thought i'd live in a house with beautiful furniture and lovely carpets - I was there a year and I was so unhappy I had to leave.
My point is that sometimes life throws you a hell of a curve ball, and you're left spinning and trying to work out what happened after it smacks you right in the face. You do not have to immediately get up and start clapping for everyone else - you can sit there spinning for a while and get your bearings. When I went through something like this my sister got a new boyfriend and was going on about how amazing it was and how great he was (he wasn't and they broke up but that's another story) and I used to want to burst into tears because I had just lost everything.
What I have realised from things is that I used to consider life this linear path, and I realise now that it isn't, it's full of ups and downs. For all you know, you could be married to the most amazing man ever in another 2 or 3 years time, you could start your own business, you could find the new hobby you never even knew you loved. I've met so many amazing people after I got out of my LTR, I felt so lost for so long, it was truly horrendous. It does change though and it does get better I PROMISE you it does, but in the meantime you have to really give yourself some grace and if things make you feel shit it is absolutely acceptable to cordially distance yourself from them and aknowledge that right now you are going through some shit.
Society kind of sucks because everyone is clapping when something amazing happens, and when it all falls to pieces they're like "oh sorry to hear" - the people who need the support are the ones who have had the fall, not the ones who are having a grand old time. Perhaps this message will reassure you that it's alright to give yourself permission to not give a fuck about Karens babyshower or Kates engagement party or Toms promotion today and that despite being happy for them, your bandwidth needs to go towards what you are dealing with right now which is a lot to handle.
I'm sorry this is so long but I do genuinely want you to give yourself a bit of leaway and realise that society is pretty annoying sometimes, and that you deserve to have support and time to get yourself on the right path. When you have your bandwidth back you can go right back to helping with the party catering, but for now it's ok to not bother.