Is there a vaccination available? I really don't want to catch feelings because it sounds dreadful.
Yes, I too want to know wtf 'Caught feelings' means.
OP you sound very very young in your attitude toward this.
Your partner cannot not go to his Brother's wedding.
You're not invited-as a PP said, you may be on all the photos and they're expecting it to not be a long term relationship. You may know/feel different but that's what they may think.
I am another one curious to know when at 23 you've had time to have two children, date a guy, then meet and become friends with his brother for a year then be with him for 2 and a half years, how does this work?
What 'support' do you think he needs at a wedding? He's going to a happy family occasion, not a funeral or for a traumatic experience of any sort.
Where would you put the children if you did go?
One thing I will say is perhaps your partner knows exactly why you're not invited, in detail and doesn't want to say, which may explain how he is being a bit elusive. I may want to know why, in your position, but I wouldn't let it concern me at all. We're not all invited to family/friends weddings/birthdays/big occasions, 'tis life I'm afraid.