Glad to hear you're feeling better. Sometimes it helps to "spill your guts" to a close friend(s) but if you have or continue to feel this way, get some help.
For some, depression won't get better or go away by itself. It would be a good idea to see your dr. and if he doesn't think you need meds you might want to see a counselor. They can determine if counseling would be helpful and all you may need is to go a few times.
I agree with the others, that you need to take back control of your life and not allow your family to make you feel like the bad person. It's to bad about your birthday, it's hurtful when siblings do things like that to each other.
As for your son's wedding, if it were me I wouldn't miss it for the world. It's understandable that you'd feel torn between your kids but they're adults and it's their job to work things out between them.
Go buy that new dress for the wedding and dance the night away. You won't regret it.
Good luck!