@CocotheLebanese,
Stop offering yourself up to her.
Quit with the sympathetic ear stuff. If you don't want to do it, then don't volunteer.
As for the ceremony/reception, you are really allowed to not go. However, receptions cost $$. If you're not going to go, tell her or whoever is footing the bill so they aren't stuck paying for your plate.
If you are going anyway, then do what thousands, nay millions of people before you have, when confronted with a party they didn't want to be at:
- Dance with anyone! I bet older men (as in the groom's grandfather) would love to
- Enjoy the food
- Sit down and talk to someone who looks equally miserable or at least alone or lonely. Male or female, young or old; it doesn't matter. Don't trash the bride or groom. Just be nice and engage in small talk. Nothing deep. "Wow, those are great flowers!" "I just love these little mushroom appetizers." "How do you know the couple?" "Have you ever been to our town before?"
- An open bar is your friend, so long as you're not driving -- so you might want to specifically make arrangements for an Uber
And finally, even if you go to the reception, you are under no obligation to stay until the bitter end. If you've been through the main course and are just dying to get out of there, then go.
The bride will be so busy and overwhelmed with everyone (and, as you noted, she's self-centered anyway), that she'll never notice.