Divorce changes everything for everyone. You just need to remember that it's hard for your parents too. I'm sure your dad would jump at the chance to take you to the fair and spend time with you, because what a shock to see your child every day one day, and the next you're seeing them every other weekend.
You ain't whistling Dixie. Going weeks on end without seeing my ex-wife, no biggie. Going two weeks without seeing my daughter is tough.
If your relationship with your father is getting stronger, let it. A lot of what I would have to say on the issue depends on the status of your mother's new relationship. If this is something that seems like it's going to be for the long haul, then you are going to have to make some adjustments in your personal life. If this is some guy she met a month ago, my advice would be not to sweat it. Chances are it won't last.
Is your mom's new boyfriend nice to you? An asshole? Indifferent? He may not really say much to you because he may not know what to say. If he's interested in a long term relationship with your mother, chances are he'll want to include you in an activity like the country fair. She may be spaced out because she has some crazy female
romantic notion about riding there on his motorcycle. If so, maybe it would be best if you go with your father. Or, go with friends. Of course, he might not have any idea what she's got in her head (this happens a lot!
) and really not have any interest in going to the country fair. He may be planning to drive, assuming all three of you are going. If he's not an asshole, mention the fair and see what his plans are. Open the dialogue and see what happens.