I assume you are in NC based on your username - if so there is no reason you should have to pay spousal support because in NC that is voided due to adultery. You have the kids the majority of the time, she left the house, she had an affair, you kept the kid's stable in their home. Each of these is a trump card. You are in good shape and shouldnt have to pay her a dime of spousal, and only pay child support if you make vastly more than her, and even then it will be limited.
If I were you I would take the full refund and file under adultery. Shop around for an attorney with experience doing this though. It will cost more up front, but its worth it not having to write her (and her future boyfriends) a check every month for the next 8 years.
Also, if you file you can slip in a 50/50 split on college costs. Probably not something she is thinking about but that could save you $100k easily.
