I'm going to break up with my girlfriend at her senior homecoming
Are you tired of her family and don't want them with you at homecoming?
Yes, her family is a pain in the ass.
I'm sorry you're not compatible with her family, but can't you wait for a better opportunity? Her senior homecoming may be one of the most important events in her young life so far, you have no right to sully it and turn it into a horrible memory for her.
May be I'm not as nice to her as I said, I will break up with her at homecoming.
That is such an important event so you really should try to wait until after that. It would not only hurt her, but she'll be embarrassed as well. If oyu can't wait till after try to do so as soon as possible.