This is another one of FOB's "I'm jealous of your boyfriend" kind of songs.

"Does your husband know the way
That the sun shine gleams from your wedding band?" -He believes the girl's spouse isn't treating her right.

The title of the song refers to a famous baseball player Pete Rose, who was busted for betting on his game. He was called a cheater. Perhaps the song title was to imply the "other guy" is unfaithful and a cheater?

"I will never end up like him
Behind my back I already am" -He promises to be faithful but he isn't sure if he is himself.

"Keep a calender this way you will always know" -When most people cheat, they do it when their spouse is working or busy. Maybe the 'calender' is her schedule.

"Its a sign its a sign its a sign its a sign its a sign but if you peaked early..." -This refers to the taboo that if the groom sees the bride's dress before the wedding day, the marriage is doomed.

That's what I got out of it. I could be wrong :/