Reagan did not want the divorce. It was his 1st wife who sued for divorce because she didn't like him devoting so much time to cleaning the Communist out of the Actors' union. From Wikipedia:
"Following arguments about Reagan's political ambitions, Wyman filed for divorce in 1948, citing a distraction due to her husband's Screen Actors Guild union duties..."
Thanks, I didn’t know that. Today you don’t even need to cite a reason (no fault).
Also, according to what I’ve read, Wyman packed Reagan’s bags while he was away on a trip and threw them out of the house. She had an affair with actor Lew Ayres while still married, but even after the affair became public, Reagan was still willing to take her back.